The Microsoft announcement re Studio Effects for external web cams is dated Sept 2025, about the same time that 25 H2 was released. So its fair to say the Preview is required. Further, the roll-out is to Intel based chips first with no timeline for AMD (or Qualcomm).
The wording of the blog is ambigious in that it talks about USB as an “additional” camera making it unclear if a USB only camera meets the requirement. If reached out to try and get clarity but I don’t know anyone in the Studio Effects area so that’s a long-shot