Thank you for posting your query on Microsoft Q&A. From above description its seems like the user is getting error while trying login to the tenant or application with a personal account.
Please do correct me by responding in the comments section.
To resolve the error, kindly refer to below doc for similar issue and TSG:
Error AADSTS50020 - User account from identity provider does not exist in tenant
If this does not work then please validate the following:
- See if you are logging onto correct directory on your tenant:
- External collaboration settings:
- Sign in to the Azure portal with Global Administrator permissions.
- Browse to Azure Active Directory > User settings.
- Under External users, select Manage external collaboration settings.
- On the External collaboration settings page, select Guest user access is restricted to properties and memberships of their own directory objects option.
- If you are an administrator, you can also try to dismiss the user risk after ensuring that the risk assessment was a false positive.
Update 2:
Seems like you were using a free version of Azure AD/Entra ID. Since Azure AD is now Microsoft Entra ID,
The free edition of Microsoft Entra ID is included with a subscription of a commercial online service such as Azure, Dynamics 365, Intune, Power Platform, and others.
So either you may get one of the above mentioned subscription or you needed P1 or P2 subscription: https://www.microsoft.com/en-us/security/business/identity-access/microsoft-entra-id#:~:text=The%20free%20edition%20of%20Microsoft,%2C%20Power%20Platform%2C%20and%20others.
Thanks,
Akshay Kaushik
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