Do you know about Flatseal? It’s an application that lets you manage flatpak permissions. Until the portals system is fully working, weakening the sandboxing using Flatseal is what a lot of people do to make the apps work correctly.
Also, if you use KDE, the settings app has flatseal-like functionality built in.
That’d be cool, but just a simple reminder in case not, that you can simply make an account on that instance. There’s no limit to what instances you’re allowed to have accounts on or anything like that, so you can always do that.
Still for cohesion I get wanting it all together.