So you can ask them what they are passionate about outside of work. Something like:

I’m really into reading sci-fi books. Is there anything you are passionate about outside your work?

If you are interested in open street maps, then you might want to check out the StreetComplete app. It will give you various quests to complete and achievements to unlock.

Kann man irgendwie die abonnierten Communities mitnehmen?

In den Profiel Einstellungen, ganz unten unter “Einstellungen Importieren/Exportieren”. Wenn das Web Frontend nicht geht kann man auch direkt über die API exportieren: https://feddit.de/api/v3/user/export_settings