Rest Outlook profile on a Windows PC
Rest Outlook profile on a Mac
Quit Outlook
Open Finder → Applications.
Right-click Microsoft Outlook → Show Package Contents.
Navigate to: Contents → SharedSupport
Launch Outlook Profile Manager.
On the Profile menu, choose "new profile"
Give it a name, such as: Outlook-New
Select the new profile.
Choose Set as Default.
Start Outlook and add the user's Microsoft 365 account again.