@noelBlanc:
Thank you. I am now studying your "script V26" and trying to work out why I cannot pair a BlueTooth device while other people can.
@Lancelot:
You have had a very good summary of the topic. It looks to me that @noelBlanc made the first discovery in getting BTH working in PE. Then WimBuilder2 and Win10XPE adapted it. For the moment, Win10XPE (2021-01-16.7z) is much stable and easy to configure. WimBuilder2 (Full.v2021-02-02) is faster, but not stable. It stopped working for many reasons.
I think currently there is a lack of a "complete" BTH plugin that can stand by its own, i.e. including all the files, drivers and registries it needs.