Hi @Dilpreet Singh , yes you can do this! You can continue using custom policies in Entra External ID to define the sign-in experience. You can take in the user's email address and authenticate based on the email domain.
External tenants can be configured using OIDC connections, similar to your current setup with B2C.
Please let me know if you have any questions and I can help you further.
If this answer helps you please mark "Accept Answer" so other users can reference it.
Thank you,
James