Everyone says Godot, but I disagree. Godot is too high level and it won't teach you much about how it all works. Godot is good if you have already mastered languages and common gaming algorithms (e.g. collisions), and you just want to get going. But as a first foray, I'd say, go with SDL. After you done something simple in SDL and learned some hands on knowledge on how things work under the hood, go with Godot or Love. That knowledge will help you troubleshoot godot better then.