Outlook/Hotmail 'Error 400' persisting after password reset and troubleshooting across multiple devices

I am locked out of my main (free) Outlook/Hotmail account due to a persistent Error 400, even after a successful security verification and password reset. This appears to be a broader issue as it affects multiple accounts and devices in my household.

System: Windows 11 on a Dell desktop

Steps already taken (no success):

• Cleared browser cache and cookies
• Tested on multiple browsers (Chrome, Edge)
• Tested on multiple devices (desktop, two laptops)
• Reinstalled the Outlook web app
• Attempted website support (death loop to change my password etc)
• Attempted phone support (automated loops)

The issue persists despite following all official Microsoft support articles.

Any advice on how to break this loop and regain access?