Uh-oh. I tried again to turn on the Sony TV that does not have an Apple TV attached and it didn't work. I went back to the Sony with the Apple TV, did some troubleshooting and looking through menus when I discovered that there was some other device paired with the Siri remote. Turns out it was the TV without the Apple TV attached. (Is this making sense???) So, somehow, that second TV of mine paired itself with the Siri remote, making it look like it was turning on via IR. Weird.That sounds promising. 😊
Can you double check if your Siri Remote is using IR for the new Siri remote Power button by holding one hand in front of the remote to block the IR signal from reaching your TV, if Power On/Off stops working, the Siri remote is sending IR to your TV (not Apple TV) for Power On/Off. Please let us know.