Error AADSTS53011:User Blocked Due to Risk on Home Tenant When Accessing BC API via Fabric Notebook

Hi kasun_rumesh ,

Thank you for reaching out to Microsoft Community.

Microsoft Fabric notebooks might be triggering a fresh token request that enforces stricter conditional access policies or identity protection policies.

Check Risky Users Report. Go to Risky Users in Microsoft Entra ID and search for the affected user.

If listed, you can either dismiss the risk, if it’s a false positive, reset the password to trigger remediation.
If the user is a guest or federated from another tenant, ensure they’ve completed Multi-Factor Authentication (MFA) and Self-Service Password Reset (SSPR) in their home tenant.
Review policies in both the home tenant and the resource tenant to ensure they aren’t blocking high-risk users.
In Microsoft Entra, go to Sign-in logs to get detailed info on why the sign-in was blocked.

Please refer to these documents which helps you to troubleshoot the issue based on the cause.
Microsoft Entra ID Protection for B2B Users - Microsoft Entra ID Protection | Microsoft Learn
Remediate risks and unblock users - Microsoft Entra ID Protection | Microsoft Learn
Your sign-in was blocked - Microsoft Entra ID | Microsoft Learn

I hope this will help.
Best Regards,
Chaithra E.