Configuring preferences and options in Outlook.com
Near as I can tell the paid Microsoft 365 does NOT have the Sync option available in the online Outlook.com. In the paid Microsoft 365 you can add additional mailboxes under the Premium settings but that is different than the Sync that users have been used to for decades.
So even if you pay for it you can't delete an existing Sync email or change the password on an existing Synced email account.
As a programmer myself there is absolutely no excuse that it was not thought through enough when they did decide to depreciate one of the most useful features of Outlook.com. Displaying and updating the sync email settings from a database is such a basic thing that any 100 level intro to programming class student would be able to handle it. That Microsoft has messed it up this bad and has not fixed it shows how incredibly bad not only their programmers are but also their Outlook product manager.
135 replies and 4000+ views in a month should tell any Program Manager that you have a HUGE problem with your software.