The suggested site https://LearningOpenGl.com is great and I've seen similar websites for Vulkan and WebGPU.
I also recommend grabbing the suggested book, Real Time Rendering, along. I've found it to be great learning material, having a well detailed chapter dedicated for all the effects used in modern renderers. Works great as a reference though it doesn't have any code samples. Doesn't concern itself too much about API details. In my learning flow, I go through a chapter and try to implement one of the techniques mentioned for the effect; usually referencing one of these web resources.
I also recommend grabbing the suggested book, Real Time Rendering, along. I've found it to be great learning material, having a well detailed chapter dedicated for all the effects used in modern renderers. Works great as a reference though it doesn't have any code samples. Doesn't concern itself too much about API details. In my learning flow, I go through a chapter and try to implement one of the techniques mentioned for the effect; usually referencing one of these web resources.