email does not appear on desktop, but does on iPhone and iPad
I have a 2024 iMac just set up. Incoming emails on a Microsoft Exchange account appears on my iPhone and my iPad, but not on the iMac?
I would remove the email account that you have with Microsoft in Mail and then re-add it.
About a month ago I did add my Outlook and Hotmail account to Mail after a server side switch was enabled and I tried it but found I prefer the Outlook app over Mail for Microsoft email accounts.