Not a complete list. But the resources I think you have to check out.
- Guided OpenGL tutorials (both available as actual books): https://learnopengl.com/ & https://antongerdelan.net/opengl/
- OpenGL reference book: https://www.opengl.org/sdk/docs/books/SuperBible/
- GLSL spec: https://registry.khronos.org/OpenGL/specs/gl/GLSLangSpec.4.60.pdf
- Mostly GLSL fragment shader stuff: https://thebookofshaders.com/
- Almost demo-scenish shader gallery: https://shadertoy.com/
- Inigo Quilez: He's doing very cool stuff on Youtube https://www.youtube.com/@InigoQuilez and his site is a goldmine: https://iquilezles.org/
- Freya Holmér: You can randomly watch a video and gain something: https://www.youtube.com/channel/UC7M-Wz4zK8oikt6ATcoTwBA