I get the error message shown in the screenshot below. Other screenshots showing that I do have access to realm management.
I logged out of my microsoft account yesterday and restarted. This allowed me to join the realm one time, but the original error came back after the one successful login. I am able to join other people's realms with no problems.
I am still experiencing this problem. Just tried to log into all 3 of my realms after logging out and restarting my computer and I got the same error for all 3 realms.