Almost exactly 1 year ago, I built a simple macOS app to run randomized photo slideshows (turns out - it's not an easy thing to do on macOS!). I got some nice initial traction (no paid ads), received user feedback, added more features, did a few releases, and after 6 months introduced a one-time fee (needed only if you want to run a slideshow with more than 150 photos; otherwise the app is free to use). And it turned out - people find it valuable and buy the license :)

I have not published it via the App Store though. It's a direct distribution (via .dmg, but it's checked & notarized by Apple so I needed to pay $99/year fee to be able to do that). I'm using Sparkle to handle the updates.