okay I just did this.
with outlook opened
go to notifications & actions in windows 10, turn off outlook notifications.
now turn outlook notifications back on.
Closed outlook
opened outlook
went to file/options/mail in outlook
I unchecked "display a desktop"
recheck "display a desktop"
sent myself a test email, the notification popped up with a sound, I clicked on it, the email popped up........
Can anybody else try this and verify if it worked for them?
EDIT: my solution ended up not working anymore after a few hours....... uninstall/reinstall seems to be best choice.