Just noticed that this might be a bigger issue and not only for me.
r/Plex - Plex Dash - Server not in list
r/Plex - Dash app not seeing server anymore
I also reinstalled the app to see if that improves the situation but now have the “???” under Server…
It apparently also was discussed here: Plex Forums - Dash app Not Showing Video Stream Details (just audio)
So happy to have this thread closed.