Yeah, SwiftUI is still immature in many areas, so each new version adds a lot of essential features. I'm not talking fancy new things, just the basic stuff that almost every app needs. The alternative is to implement through the older UIkit which is slower to do, especially for people like me who don't really know UIkit from before.

As for Avelon I'm using a few key features introduced with v16. Since I'm just one dev I prioritized polish and features over supporting older versions which would take much more time. Yeah, it sucks if you're stuck on iOS 15, but that's just what I decided to prioritize.

Also, as the developer of Lemmios, it is somewhat negligence on my part (not saying this is true for any of the other app developers, just me), we all google when we code and generally the newer features make things much easier so it is really hard to google older features since they are harder to implement and get quite buried. I also think for me at least my apps start as passion projects I don't really expect anyone to use so I forget that iOS versions under my current one exist lol, it's a lot easier to start on 16.0 and stay on 16.0 forever than go lower after the project has started, sorry.