I have three Apple TV 4K 2021 boxes, all running tvOS 16.0 (20J373) and all connected via ethernet. A week ago one of them inexplicably started a simultaneous WiFi connection in addition to ethernet, using a separate MAC address. There was consistent network traffic on both connections to my router, the bulk of it on the wired connection and an average of only ~30 kbps on the wireless connection. The tvOS network setup screen always showed an ethernet connection instead of WiFi. Restarting the router and the ATV box didn’t get rid of the WiFi connection but when I disconnected the ethernet cable from the ATV it immediately switched to the WiFi connection, so I selected it and clicked “Forget Network”. I plugged the ethernet cable back in and the ATV reconnected to the router only via ethernet; the rogue WiFi connection hasn't happened since then.