so, I'm making a terraria-like game in unity using c# which has procedurally generated tilemaps and i have this script attached to a grid:

using UnityEngine;
using AccidentalNoise;
using System.Collections.Generic;
using UnityEngine.Tilemaps;
using System;

public class CompileTerrain : MonoBehaviour
{

    public TileBase dirtTile;
    public TileBase grassTile;
    public TileBase stoneTile;

    public List<GameObject> fractalLayers = new List<GameObject>();

    public Tilemap grid;
    public int width;
    public int height;

    public float seed;
    public int caveSmoothness = 2;

    void Start()
    {
        grid.ClearAllTiles();

        int touchCount = 0;
        Vector3Int newPos;
        double nx, ny;

        ModuleBase combinedTerrain = CavesAndMountains((uint)seed);
        List<Vector3Int> terrainCoords = new List<Vector3Int>();
        SMappingRanges ranges = new SMappingRanges();

        for (int x = 0; x < width; x++)
        {
            for (int y = 0; y < height; y++)
            {
                nx = (ranges.mapx0 + ((double)x / (double)width) * (ranges.mapx1 - ranges.mapx0)) * 3;
                ny = (ranges.mapy0 + ((double)y / (double)height) * (ranges.mapy1 - ranges.mapy0)) * 3;

                if (combinedTerrain.Get(nx, ny) > 0f)
                {
                    terrainCoords.Add(new Vector3Int(x, height - y, 0));
                }
            }
        }

        List<Tuple<int, int>> neighbors = new List<Tuple<int, int>>() {Tuple.Create(1, 1), Tuple.Create(-1, -1),
                                                                       Tuple.Create(0, 1), Tuple.Create(1, 0),
                                                                       Tuple.Create(0, -1), Tuple.Create(-1, 0),
                                                                       Tuple.Create(-1, 1), Tuple.Create(1, -1)};

        for (int index = 0; index < terrainCoords.Count; index++)
        {
            if (index == terrainCoords.Count)
            {
                break;
            }

            touchCount = 0;

            for (int posAdd = 0; posAdd < neighbors.Count; posAdd++)
            {
                newPos = new Vector3Int(terrainCoords[index].x + neighbors[posAdd].Item1, terrainCoords[index].y + neighbors[posAdd].Item2, 0);
                touchCount += terrainCoords.Contains(newPos) ? 1 : 0;
            }

            if (touchCount < 2)
            {
                terrainCoords.Remove(terrainCoords[index]);
            }

        }

        for (int j = 0; j < caveSmoothness; j++)
        {
            for (int x = 0; x < width; x++)
            {
                for (int y = 0; y < height; y++)
                {
                    if (!terrainCoords.Contains(new Vector3Int(x, y, 0)))
                    {
                        touchCount = 0;

                        for (int posAdd = 0; posAdd < neighbors.Count; posAdd++)
                        {
                            newPos = new Vector3Int(x + neighbors[posAdd].Item1, y + neighbors[posAdd].Item2, 0);
                            touchCount += terrainCoords.Contains(newPos) ? 1 : -1;
                        }

                        if (touchCount > 1)
                        {
                            terrainCoords.Add(new Vector3Int(x, y, 0));
                        }

                    }

                }

            }
        }

        foreach (Vector3Int blck in terrainCoords)
        {
            grid.SetTile(blck, stoneTile);
        }

        terrainCoords.Sort((x, y) => x.x == y.x ? x.y.CompareTo(y.y) : x.x.CompareTo(y.x));
        terrainCoords.Reverse();

        TileBase selectedTile;
        int depth = 0;
        int lastx = 0;
        int lasty = terrainCoords[0].y + 1;

        foreach (Vector3Int blck in terrainCoords)
        {
            depth = blck.x != lastx ? 0 : depth;
            lasty = blck.x != lastx ? blck.y + 1 : lasty;

            selectedTile = depth < 4 ? grassTile : stoneTile;
            selectedTile = 3 < depth &amp;&amp; depth < 30 ? dirtTile : selectedTile;

            grid.SetTile(blck, selectedTile);

            lastx = blck.x;
            depth += lasty - blck.y;
            lasty = blck.y;
        }

        int layerNum = 1;
        List<Vector3Int> posList = new List<Vector3Int>();

        foreach (GameObject layer in fractalLayers)
        {
            GetPerlinLayer component = layer.GetComponent<GetPerlinLayer>();

            for (int k = 0; k < component.populateCount; k++)
            {
                layerNum++;
                foreach (Vector3Int pos in component.GetFractalCoords(width, height, (uint)(seed * layerNum)))
                    if (grid.GetTile(pos) != null &amp;&amp; grid.GetTile(pos) != grassTile)
                    {
                        grid.SetTile(pos, component.defaultTile);
                    }
            }
        }
    }

    public static ModuleBase CavesAndMountains(uint seed)
    {
        AccidentalNoise.Gradient ground_gradient = new AccidentalNoise.Gradient(0, 0, 0, 1);

        // lowlands
        Fractal lowland_shape_fractal = new Fractal(FractalType.BILLOW, BasisTypes.GRADIENT, InterpTypes.QUINTIC, 2, 0.25, seed);
        AutoCorrect lowland_autocorrect = new AutoCorrect(lowland_shape_fractal, 0, 1);
        ScaleOffset lowland_scale = new ScaleOffset(0.125, -0.45, lowland_autocorrect);
        ScaleDomain lowland_y_scale = new ScaleDomain(lowland_scale, null, 0);
        TranslatedDomain lowland_terrain = new TranslatedDomain(ground_gradient, null, lowland_y_scale);

        // highlands
        Fractal highland_shape_fractal = new Fractal(FractalType.FBM, BasisTypes.GRADIENT, InterpTypes.QUINTIC, 4, 2, seed);
        AutoCorrect highland_autocorrect = new AutoCorrect(highland_shape_fractal, -1, 1);
        ScaleOffset highland_scale = new ScaleOffset(0.25, 0, highland_autocorrect);
        ScaleDomain highland_y_scale = new ScaleDomain(highland_scale, null, 0);
        TranslatedDomain highland_terrain = new TranslatedDomain(ground_gradient, null, highland_y_scale);

        // mountains
        Fractal mountain_shape_fractal = new Fractal(FractalType.RIDGEDMULTI, BasisTypes.GRADIENT, InterpTypes.QUINTIC, 8, 1, seed);
        AutoCorrect mountain_autocorrect = new AutoCorrect(mountain_shape_fractal, -1, 1);
        ScaleOffset mountain_scale = new ScaleOffset(0.3, 0.15, mountain_autocorrect);
        ScaleDomain mountain_y_scale = new ScaleDomain(mountain_scale, null, 0.15);
        TranslatedDomain mountain_terrain = new TranslatedDomain(ground_gradient, null, mountain_y_scale);

        // terrain
        Fractal terrain_type_fractal = new Fractal(FractalType.FBM, BasisTypes.GRADIENT, InterpTypes.QUINTIC, 3, 0.125, seed);
        AutoCorrect terrain_autocorrect = new AutoCorrect(terrain_type_fractal, 0, 1);
        ScaleDomain terrain_type_y_scale = new ScaleDomain(terrain_autocorrect, null, 0);
        AccidentalNoise.Cache terrain_type_cache = new AccidentalNoise.Cache(terrain_type_y_scale);
        Select highland_mountain_select = new Select(terrain_type_cache, highland_terrain, mountain_terrain, 0.55, 0.2);
        Select highland_lowland_select = new Select(terrain_type_cache, lowland_terrain, highland_mountain_select, 0.25, 0.15);
        AccidentalNoise.Cache highland_lowland_select_cache = new AccidentalNoise.Cache(highland_lowland_select);
        Select ground_select = new Select(highland_lowland_select_cache, 0, 1, 0.5, null);

        // caves
        Fractal cave_shape = new Fractal(FractalType.RIDGEDMULTI, BasisTypes.GRADIENT, InterpTypes.QUINTIC, 1, 4, seed);
        Bias cave_attenuate_bias = new Bias(highland_lowland_select_cache, 0.65);
        Combiner cave_shape_attenuate = new Combiner(CombinerTypes.MULT, cave_shape, cave_attenuate_bias);
        Fractal cave_perturb_fractal = new Fractal(FractalType.FBM, BasisTypes.GRADIENT, InterpTypes.QUINTIC, 6, 3, seed);
        ScaleOffset cave_perturb_scale = new ScaleOffset(0.5, 0, cave_perturb_fractal);
        TranslatedDomain cave_perturb = new TranslatedDomain(cave_shape_attenuate, cave_perturb_scale, null);
        Select cave_select = new Select(cave_perturb, 1, 0, 0.75, 0);

        return new Combiner(CombinerTypes.MULT, cave_select, ground_select) as ModuleBase;
    }
}

which i have so graciously borrowed and modified from the fine folks at accidental noise, and i made an empty gameobject which i attached this script to:

using UnityEngine;
using AccidentalNoise;
using System.Collections.Generic;
using UnityEngine.Tilemaps;

public class GetPerlinLayer : MonoBehaviour
{

    public TileBase defaultTile;
    public float threshold = 0.5f;
    public int populateCount = 5;

    public List<Vector3Int> GetFractalCoords(int width, int height, uint seed)
    {
        double nx, ny;

        ModuleBase combinedTerrain = new Fractal(FractalType.FBM, BasisTypes.GRADIENT, InterpTypes.QUINTIC, 6, 2, seed);
        List<Vector3Int> fractalCoords = new List<Vector3Int>();
        SMappingRanges ranges = new SMappingRanges();

        for (int x = 0; x < width; x++)
        {
            for (int y = 0; y < height; y++)
            {
                nx = (ranges.mapx0 + ((double)x / (double)width) * (ranges.mapx1 - ranges.mapx0)) * 3;
                ny = (ranges.mapy0 + ((double)y / (double)height) * (ranges.mapy1 - ranges.mapy0)) * 3;

                if (combinedTerrain.Get(nx, ny) > threshold)
                {
                    fractalCoords.Add(new Vector3Int(x, height - y, 0));
                }
            }
        }

        return fractalCoords;
    }
}

and i attached different colored square sprites for each of those gameobjects, and saved them as a prefab. Once i had that prefab, i attached that to the fractalLayers list in my previous script to generate ores. And although it runs fine on a lower scale, I cant run it on a larger scale. And since there's no cure-all for making code run faster (aside from refactoring, which i don't know how to do), and i probably could've made parts of my code more efficient since I'm a novice, i would really like some insight from the eyes of a professional on how to make my code run better. I know i didn't explain everything about my project but its really just a bare-bones project those are the only scripts and unique parts about it, you can just infer what i did and fill in the blanks. Any help is appreciated. And if you could give me the extra push along with some information on the subject, I would love to have some videos recommended along with your insight to guide me along this process, since i am more of a visual learner. Thank you! =)

The main thing is to avoid doing memory allocation - that means you should use structs where possible for small objects, set the capacity of lists in advance instead of just letting them re-allocate automatically, avoid foreach in favour of for when possible (as sometimes foreach has to allocate an iterator), etc.

Another thing to do is to precalculate some of this data. Looking at your CavesAndMountains function, most of the data in there has nothing to do with the game object it's on, or the value passed into the function - which means you can precalculate the data and store it somewhere instead of regenerating it each time you call Start. This might require writing an editor tool, however.

Beyond that, you should refactor your code into separate, smaller functions, and then use the Unity profiler to see which ones are the slowest - that will help you focus on where the real problems are.