Thanks for reaching out.
I understand you are looking to update your B2C web application with user friendly name which can be achieved by enabling custom domain in Azure AD B2C. B2C custom domain functionality works with Azure Front Door.
Refer to configure custom domain in Azure AD B2C: https://learn.microsoft.com/en-us/azure/active-directory-b2c/custom-domain?pivots=b2c-user-flow
App registration endpoints specify the default domain of B2C which further invokes the front door to resolve custom domain name. You cannot edit the default endpoints of B2C to point to user friendly name directly.
Hope this will help.
Thanks,
Shweta
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