Hi
There is still a gap or deficiency when it comes to federated domains and cloud users.
If a cloud user UPN is set to use federated domain - user password cannot be changed.
Azure error: Unfortunately, you cannot reset this user's password because password writeback is not enabled in your tenant.
If I try to set such mailbox to be cloud managed, it also fails.
Exchange error: The object is not being synced from onpremises AD. This parameter change is not allowed for this object
This is still a problem (it was for years...)
It is not possible to create a room mailbox using federated domain, and then enable that accounts to become Teams room.
(Account must be enabled and must have password (re)set to provision it in Teams Room management portal)