Where to go after learning the basics.

So I have learned all or most of the fundamentals. I have been using python for quite some time, recently moving over to c# and then c++ with the goal of creating my own game library/framework (for learning purposes. I use godot for my actual games and going to move over to unreal to use c++ more). As i have said, I know all or most of the basics up to OOP. Now I want to move away from the typical console apps created when learning. I am just stuck on where to start... I cant find much material on sdl3 and I struggle learning by just reading docs(working on improving in this area). Hell I dont even know if I should be starting with sdl. I would like to learn graphics programming because thats what peaks my interest at the moment. Even if it is to create a gui library I would love that! I realize I wont be doing all that out the gates but I would just like some info and recourses to take the first step toward my goal.

Thanks in advance!