I found that setting deadlines solves most scope creep problems. Anecdotally, I am more likely to complete a project for a game jam or programming contest (which come with hard deadlines) than finishing an open-ended project.

See also "Why does the C++ standard ship every three years" (as opposed to ship when the desired features are ready):

https://news.ycombinator.com/item?id=20428703 (2019-07-13, 220 comments)