'You cannot play on Realms...'

I can see that there are a plethora of tickets with the above tagline, but nothing I've tried so far has worked:

I have so far done the following:
Checked account date of birth. It is set to the correct date of birth in the ~1980s
Set all account settings to 'Adult' / 'Unfiltered'
Set other account settings in Xbox X/S to 'Allow'
Logged out of the Xbox itself
Restarted the Xbox several times
Closed Minecraft and restarted it several times

Everything in game points toward an Xbox game pass. Which is a rip off. I pay for the realm monthly already. I don't see why I should be paying more than double the realm cost, just to play one game. frustrated