Using classic Outlook for Windows in business environments
Located in Canadian east coast as well and using Windows 11 and outlook 365 version 2209 with the same issue. When I open the certificate and check the root and intermediate, they show up as ok.
Serial Number for the cert is : 0f12dc8955821d6d936bcf34e50f60c5
EDIT:
I tried removing modern auth and reactivated it. Will give let you know if the issue re-occurs.