Looks like (thanks to the EU again) that iOS will support side loading apps shortly which should at least give options should an app be removed from the store. As for the reality …. I guess we just need to wait and see https://www.macrumors.com/2023/04/17/app-sideloading-support-coming-ios-17/
Wefwef (https://github.com/aeharding/wefwef) is worth a look. It’s a PWA that is very similar to Apollo in looks. Pretty amazing what’s been done in a PWA