I use the brick app: https://getbrick.app/, and it works pretty well, but they have this weird bug where selecting certain apps on a block list crashes the app. They have a pop-up indicating that it's some apple-related bug, which I find kind of hard to believe. Is this something that also happens in your app?
I haven't noticed this on my personal use. It does seem like they use the family picker activity built into iOS. So maybe the issue is here as well.