I had this exact problem. It started after all the sound stopped abruptly in the middle of an Apple Fitness workout. (I have two home pod minis connected for sound -- I do not use the TV's speakers.) I stopped the workout and navigated to Settings, and suddenly the volume of the TV shot up uncontrollably to 100 and stayed there. My TV shows a light when it's receiving an IR signal, and it was being blasted by the Apple Siri remote. Covering the front of the remote stopped it, so it's clearly IR.
None of the troubleshooting steps in Apple Support worked. Turning off all the CEC, IR, etc. stuff didn't work. The remote was stuck blasting an IR signal continuously.
In desperation, tonight I updated to tvOS 15.2 (19K53) and the IR blasting stopped. I have no idea if the update fixed it or just restarting the Apple TV fixed it. And I have no idea if it will stay fixed.
I'm posting this in hopes that other people find this information useful.