BGFX and Forge are great, but you might also take a look at Sokol as a really absolutely lean and mean graphics layer.

https://github.com/floooh/sokol

I study this book to make my simple game engine: Build your own 2D Game Engine

This book uses WebGL and JavaScript. I rewrite examples to TypeScript/WebGL and C#/OpenTK

I like this book too: C# Game Programming: For Serious Game Creation

I wrote this clone of Pong game in C# and TypeScript. I use BMFont for fonts.

You can play here: https://8observer8.github.io/webgl10-ts/pong2d-from-noobtuts/