Hi @矢野 尭生 ,
maybe this is helpful:
..., we will still continue to support Azure AD B2C as a separate product offering with no change in SLA, and we’ll continue investments in the product to ensure security, availability, and reliability.
Source: Why is Azure AD B2C not part of Microsoft Entra External ID?
(If the reply was helpful please don't forget to upvote and/or accept as answer, thank you)
Regards Andreas Baumgarten