but isn't unity for designers??
I don't know ,but should a programmer use unity??
Unity is for people who want to finish games. Unless you're using a third-party add-on for visual scripting you still need to program to make games with Unity, so it's absolutely fine.
If you're looking for alternatives you might also try using Unreal Engine.
If you want to experience lower level programming go right ahead and use a library such as MonoGame, SFML, SDL, etc., but there's no reason not to continue using Unity if you're doing well with it so far.
Especially given you mention not getting into "hardcore development" I think just continuing to make games is probably the best option for you.