
Turn Off the slider for all the options Mobile (Exchange ActiveSync), Outlook on the web, Outlook desktop (MAPI), Exchange web services, POP3, and IMAP. Select the user mailbox from the list and then, in the Details Pane (on the right-hand side), select Manage email apps settings under Email apps.Go to the Exchange admin center > Recipients > Mailboxes.

If you have email as part of your Microsoft 365 subscription, sign in to the Exchange admin center and follow these steps to block your former employee from accessing their email.

I wouldn't try with Windows support, they don't have the best fame. Office 365 support will help You with that. If so, You have to remove the license via Powershell. Blocking an account can take up to 24 hours to take effect. Go to control panel -> credential manager -> windows credentials and check if that account is there.
