Hi @Segev Finer (Swimm)
I understand that you are trying to have users self-register as a member instead of a guest to the Azure Portal via an external identity user flow.
Microsoft Entra B2B user and guest user are synonymous. Therefore, a Microsoft Entra B2B collaboration user is added as a user with User Type set to Guest by default. However, in some cases, the partner organization is a member of a larger organization to which the host organization also belongs. If so, the host organization might want to treat users in the partner organization as members instead of guests. You can use the Microsoft Entra B2B Invitation Manager APIs to add or invite a user from the partner organization to the host organization as a member.
For reference: https://learn.microsoft.com/en-us/entra/external-id/user-properties#can-microsoft-entra-b2b-users-be-added-as-members-instead-of-guests
If you're an admin, you can choose to invite the user as member.
"invitedUserType": "Member"
Follow the document for more information: https://learn.microsoft.com/en-us/entra/external-id/customize-invitation-api
Hope this helps. Do let us know if you have any further queries.
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