I'll say that I haven't taken a game beyond a game jam myself yet, much, but I have done that 8 times now, and when I think about the Grenade example OP gave, I

I'll say that I haven't taken a game beyond a game jam myself yet, much, but I have done that 8 times now, and when I think about the Grenade example OP gave, I believe myself competent to pull it off either in a M-F week of side-project time, or inside of a weekend of the same, depending on assets of course. Godot does take a little bit to learn, but it is quite rewarding. There are a number of larger side projects, game and no, that I've either completed or abandoned over the years, and, like you said, scoping down has been a primary way to help actually get them done. But, I've also just now found a time slot to work on something consistently in, which has made a big difference. Many folks don't account for how much "project management" is a key skill in efforts like this.