My most successful (also most enjoyable, also earned me the most money) project is a tiling window manager I wrote for Windows, which I have now also ported to be cross-platform on macOS

I just built what I needed for myself - there was nothing that fit my needs when I started using Windows

Similarly, now that I'm using macOS again, I want a seamless cross-platform experience, so I made the same project cross-platform

I don't think my brain is wired in such a way that I can come up with project ideas that are divorced from something I personally have a need or desire for