Would it be a good idea to master OpenGL 4.5, as I am doinng a great job. But still I want some strong background in library for Input / Sound mainly as well. Would SDL be a good choice for both input and sound on Windows / Linux / Android mainly, I want something to work all around all the operating systems and still be fairly light weight compared to opengl. I seek to develop in the future for IOS to just never got there yet.

Yes, SDL plays WAV files quite easily anyway, and it also handles keyboard/mouse/controller input. I use it with OpenGL 4.6.

See this example for some simple code.

I just prefer to use 4.5 code for my glsl cause i got a book on shaders (shader cookbook( and that coveres it very welll, but I also read the red book. was a neat expeirence… to say the least.