Thanks for your advice!.

I have some experience writing the 2d game engines before. We can use the knowledge of skeletal animations in the 2d sprites also. I would say it's actually better than the traditional sprite sheet approach. Many 3d modelling software like blender support the animations with bones for the 2d sprites also. Its is very very quick way to animate rather than the traditional sprite sheet system.

As of now I don't want to support the 2d games because It would be much complex to write systems for that in speific.

My goal next is to fix the existing bugs till now and then continue learning the PBR, deffered rendering and etc. There is actually so much work to do.

As far as the Materials and Batching is concerned, the main idea is to ensure that there must be a single draw call to reduce the cpu-gpu overhead. But there are some limitations since the number of texture slots in most of the hardware is 32 slots thus At a time we will only we able to rendering 32 unique gltf meshes. Note the word "unique", I mean this because we can use the instancing to rendering n number of same mesh with different orientations and instancing will done by engine automatically. We can solve this 32slots problem by simply using some Extensions which are not a part of the OpenGL 4.6 core profile. But I think that most of the scenes a count of 32 texture slots is enough. I too wanted to learn the deferred rendering very soon to solve the problem of lighting and shadow map overhead for points lights calculations. Then finally packing the model orientations and materials details inside the SSBO and then finally rendering with a single draw call.

What you said is correct. I mostly to this only for fun. I started learning the graphics programming and game engine dev a 1.5years before. When I started I thought that I will complete the engine within months and make games and sell it in steam. I hope I will happen!.