That's totally weird. It is the mail provider that insists on an app password if one is required, not the client.
When you set up Windows 11 did you enter/make a Microsoft Account username and password?
If you did have you tried using that as the app is from the Microsoft store so it may require to verify via your Microsoft account.
Hi
Thanks for the suggestion. Yes, I do have a Microsoft account and have tried that, but what you suggest doesn't work. It all works fine with my Outlook email address, as does old Outlook. Frustrating !