Either there is no default mail client ...... Outlook 365 throws error message

I am doing a clean install of Windows 11 on a new ThinkPad P16s.
I have installed Microsoft 365 and now Outlook is throwing the attached error message.
I have set Outlook as the default for all file types listed under Settings / Apps.
There are many instructions in various forums to modify registry entries, but they all don't seem to work reliably.

Does anyone know what is causing this message and how to resolve the root cause?
Thanks a lot for any hints.

I can only tell you what I myself have done.
After several years, of using MS Office, and putting up with all the MS Bull Sh**, and their incessant updates, my own PC Guru suggested that I try Open Office. I did! Uninstalled MS Office that same day and never looked back.

Now, to replace Outlook Express, which I used as my one and only email program for many years, today I use "O.E. Classic" which is nearly a clone of Outlook Express. The FREE version works great for one or two email accounts.

Good Luck
TM