Thank you for your post!
From your support request concerning Cosmos DB and Azure B2C id_tokens. Our Azure B2C PG team provided an update saying that this is unsupported and is currently not on their Azure B2C Roadmap. You were then redirected here to create a feature request on Microsoft Q&A so others in the community can up vote this thread.
I've passed this along to our engineering team and will update as needed. Additionally, I'd recommended continuing to use our User Voice forum for feature requests so our engineering team can take a look into implementing this.
Thank you for your time and patience throughout this issue.
Please remember to "Accept Answer" if any answer/reply helped, so that others in the community facing similar issues can easily find the solution.