Hi @Zoran Milanovic ,
Adding a federated OIDC identity provider is currently only supported in in Azure AD B2C tenant, which supports allowing sign in via external federated OIDC IDP identities. (See Creating Azure AD B2C tenant and Add OIDC Identity Provider to B2C tenant \ user flow) .
In an Entra Workforce tenant, under External Identities you can invite B2B guest users via SAML\WS-Fed Federation feature, where OIDC is not supported.
If you are planning to invite external users to an Entra Workforce tenant and those external users have an OIDC IDP you should use B2B Guest Invitations ( Add a guest user and send an invitation )
That said, if you need to add Entra External ID Custom OIDC external identity provider support, there is a workaround option that I will send to you in a private message.
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