Cross Server Endgame

Is it possible for me to play endgame with friends (lvl 50+) on cross servers. So lets say they’re on Danube and I’m on Galatur, am I still able to do like dungeon raids together? Or is it required for me to be on their server to be in a party?

The only thing you can’t do together is open world stuff everything else is cross server

What is included in open world stuff?

I’m kinda new so I’m just asking. Any help is appreciated. So like would open world be like me physically being there with friends in that server?