Hi @Bjarne Muri ,
Thanks for reaching out.
Your understanding is correct here. B2C does not support PKCE for external IDP’s. The reason being B2C would be consider a “confidential client” in respect to OAuth/OIDC.
I checked with product team and currently it is not supported in any way.
This idea is already posted on Azure Feedback Portal, which is monitored by the product team for feature enhancements. I would suggest you to upvote that for greater visiblity.
Thank you for your time and patience throughout this issue.
Thanks,
Shweta