To cut a long story short I have an (older) Microsoft account with my work email address.
Also have a newer "Workplace or school account" setup for Teams - same email.
Since the new one was setup I've had password pop-ups in Outlook. I've signed out of the Microsoft account everywhere I can. Now I get this regular pop-up:
Type the email of the account you would like to use to open this document.
This type of account doesn't work with this particular service. Please enter an email address or phone number associated with a different account.
The email in the box is my address so this is nonsense. Email does seem to work apart from this annoyance - any ideas?