I think a fix for this behaviour landed but isn’t shipped yet:
the mail app is in a stopped state when an account is removed via system settings, it does not receive the event. This causes a desynchronized state where the app continues to display data for an account that no longer exists.
This fix reintroduces explicit broadcasts for account lifecycle events
There was a duplicate notification thread recently where in the (since removed) video one could see the account coming back. The merge request explains this and a 2023 thread: