If I'm on PS5 can I play with my Xbox or PC friends and vice-versa? (Kiln)

As far as partying up goes, people logged in on PSN accounts on PS5 can only team up with other PSN friends. The PC and Xbox versions all use Xbox accounts, and can team up together.

However, matchmaking is completely cross-platform, so you will be able to matchmake into the same matches as PSN players if you're on Xbox or PC, and vice-versa.