Hi,
This official Microsoft documentation walks you through gathering sign-in details, analyzing failure reasons, and applying fixes.
https://learn.microsoft.com/en-us/entra/identity/monitoring-health/howto-troubleshoot-sign-in-errors
if you want a live agent you can go to this link:
https://support.microsoft.com/en-us
1.Go to Microsoft Support – Contact Us.
2.Scroll down and select Get Help → Contact Support.
3.When prompted to sign in, choose I can’t sign in or Skip sign-in.
4.Select Microsoft Account as the product.
5.Under Need more help?, choose Chat with a support agent or Request a call back.
I hope this helps!