Using Outlook for Android for personal email and calendar management
THE ANSWER FOUND!!!!!!!!!!!!
Nothing helped me, even uninstalling/reinstalling etc... UNTIL I finally found someone who had the answer.
On my Samsung S24+, but I'm sure it will be comparable to other Android phones:
Go into Settings (gear icon)
Scroll down to "Accounts and Backup" (on my phone) with sub heading "Manage Accounts . Smart Switch"
Click "Manage Accounts"
Delete the offending email account(s) from the list.
Try adding the email account to Outlook again.
Worked perfectly for me - THE VERY FIRST TIME!
Didn't have to restart the phone or nothing.
I hope this helps someone - pass it on.