Apple doesn't address this anywhere I believe, or have I missed something. Any update on your part, have you got around this issue ?

UPDATE. Bought the new MBP 14’ with 10 Cores. Xcode 13.1 killing battery in a bit more than an hour. An seems there’s no way to use Xcode 12.5.1 on MacOS Monterey. Way to go Apple 🙌