I have a similar problem- Outlook 2016 is not recognised as default email app although in the defaults settings it is! The MailTo command is inoperable. I installed eM Client and that is not affected in the same way. Is this an Office 2016 problem or something that Win 11 is responsible for? I have also done a local repair on Office 2016 but no joy.
A very puzzled non-techie...
Peter Brooke