I've historically had a similar problem. I could never finish a game, not because I kept on having new game ideas, but because I always wanted to go back and redo something about the code. It boils down to the same thing, though. It got so bad that I gave up on making games for a couple years, and I've just come back to it this year. Finishing games is a skill, and you hone that skill by practice.
Something's that helped me a lot are external anchors. Make a game for a jam! Jams have deadlines, and when you have deadlines you have to finish things. Also, work with other people! When you work with other people you have to finish things. You can't just jump to another game and leave the other person hanging.
Alternatively, make a really small game. Make a game that's so small that there's no way you couldn't finish it. Then, once you've done that, make a slightly bigger one. It's all about practicing a skill.
My recommendation is to make a game for One Game a Month, and maybe even collab with someone! Having external motivators to hold you to finish a game is extremely helpful. Or at least, it was in my case. But I think it'll be helpful to you, too.