There's 0 mention of keyword "tor" or "onion" on it's documentation though https://docs.btcpayserver.org/Wabisabi/. Although i didn't watch included youtube video.
Yes, it doesn't appear the docs are extremely thorough for the coinjoin plugin. Here's the big red /!\ warning message that appears in BTCPay Server if you try to coinjoin with Tor off: https://github.com/raspiblitz/raspiblitz/issues/3729