That’s annoying! I’m using Graphene and I just installed KDE Connect from F-Droid to test, which didn’t trigger, however it did bounce me for using Heliboard. Changing to default keyboard and reloading worked, ie it can only see my currently active one.

Using Shelter to set up a second profile, or the new Private Space feature on 15 may help provide isolation.

Halifax/ Bank of Scotland/ Lloyds does an integrity check that rejects Graphene or LineageOS phones completely.

You should have a look for capture the flags for penetration testing.

TryHackMe currently has a free Christmas program which has a beginner focus and outside of that they have a mix of free and paid for content (don’t be tricked into feeling you need to pay if you just want the free content, navigate about a bit)

I’ve done some of the content and CTFs at HackerOne and I have heard of people liking HackTheBox too although I haven’t done anything over there myself.

Hopefully that gives you some inspiration and guidance to get started!