Hi @Carl Cobon ,
Good day!
Thank you for posting to Microsoft Community!
Based on your description, I understand you got a constant "Add a Service" popup in Outlook. You have already tried many common solutions, but it did not work.
Please kindly delete the account and re-add it in Control Panel as screenshot below to see if it works.
Also, you could try to delete the Outlook Profile and Create an Outlook profile - Microsoft Support.
However, it is most likely related to the problem on the backend side. If the above does not work for some reason, to check further and help you more efficiently, it is suggested to raise a ticket to contact our technical team via Microsoft 365 admin page Get support - Microsoft 365 admin | Microsoft Learn. Since we are from the community team, and we don't have that permission and resources to check this account issue from the backend side.
If the answer is helpful, please click "Accept Answer" and kindly upvote it.