Outlook integration error (skype on-prem) after migrating mailbox to O365

Im working on a problem ticket where users are reporting an issue where they keep getting the Exchange credential popup in Skype after migrating their mailbox to O365.

They were using domain\netID and password prior to the migration.   I suggested that they delete their cached credentials and use UPN and password but that didnt seem to work.

Is having a user with Skype on-prem with Exchange Online a supported configuration?     (FYI...I plan on migrating these users from Skype on-prem direct to TeamsOnly mode later this summer).