Hi Walter,
Thanks for reaching out about Outlook forcing you into a Yahoo sign‑in loop and I understand how frustrating it is when you cannot even open the app to get the help you need. This kind of issue often happens when Outlook is trying to authenticate an account in the background even if that account is no longer active or properly synced. Another solution you can try is starting Outlook in Safe Mode so it opens without loading connected accounts or add‑ins.
Safe Mode lets Outlook launch with only the essentials which can bypass the Yahoo login prompt long enough for you to adjust your settings. You can do this by holding the Ctrl key while selecting the Outlook icon and choosing to open it in Safe Mode, then removing the Yahoo profile or creating a new one from the Mail control panel outside of Outlook. Once Outlook opens normally again it should stop asking for Yahoo credentials.
Before we go further do you recall whether this started after a password change, an app update or adding a new email profile?
I hope this answer is helpful if you have further questions feel free to reply back
Regards,
Marcelo