Someone else posted this as well. It started for me on Monday when the Siri Remote suddenly stopped working. But it only happened with the ATV 4K that uses the Siri remote. It does not happen with the ATV 4k that has the older remote. I had to repair the remote. The, rebooted ATV. Then, removed me from ATV, reset ATV and turned it off, unpaired the HomePods, reset them, and repaired them, turned on ATV and thought I paired them... the only noise was me cussing. I read the article 6x6 cited and followed the instructions TWICE. I have a spare old remote and am going to see if I can pair it and if that solves the problem for me. I like it better anyway...
There has to be a solution that does not involve buying a new ATV or new HomePods.