Using Classic Outlook on Windows for personal email, calendar, and contact management
Thank you Dean for submitting your case.
At this point, is quite certain that the issue is rooted to Windows 11. All my customers with windows 10 haven't experienced this issues at all. Not all of my customers upgraded from win10 to win11 have also experienced the problem. It's something that affect only windows 11 upgraded from win 10 and with Office 2016/2019 and not M365.
Unfortunatelly I can't reverse back to Windows 10 because they use PC at work and they cannot wait.
I will try with Microsoft365 upgrade demo (if it exists)
Sincerely,
Massimo