Migrated from Microsoft 365 to WorkMail. Get prompted for old account

I just migrated a domain from Microsoft 365 Exchange to WorkMail. All seems to be work ok except I have 3 Macs using the latest Outlook for Mac to get mail. I can get signed into WorkMail okay but I keep getting prompted to sign into an account that looks like Microsoft 365. I have reset Outlook and deleted storage on the Macs but they still continue to prompt for this old account. I'm stumped. I'm not sure where Outlook is finding this old account.