If you are wanting to learn how to create games I suggest using the language most tightly coupled with the game engine you want to create games in. In Godot's case that would be GDScript. You're going to get a lot "for free" writing in GDScript. You'll be able to do some things in 1 line of GDScript, where in C++ it may take you 4-5 lines to accomplish the same task. Performance is not going to be an issue, and if it is, 90-95% of the time it's going to be caused by how you solved your problem, not the language you wrote your program/game in.
Asking that question suggests that you're new to programming as a whole. If you want to get your feet wet with multiple different languages while learning the basics of programming, I suggest you check out the free CS50 course that Harvard provides: https://cs50.harvard.edu/college/2021/spring/