what if you have more than 10 devices in your smart home?

Yes, that was my issue. I had thought the too many devices error I was getting was for what showed under my Apple ID, but those weren't the devices they were talking about. Apparently some of my old/sold computers were still authorized in ITUNES. I was mislead by the red herring that I had 10 devices listed as being authorized under my Apple ID (only one of which was a computer), but apparently, in ITunes (which I don't use ever) I had the limit of 5 COMPUTERS authorized from years ago that had screwed this whole thing up. Apple tech support was surprisingly helpful and had me deauthorize them and now everything is working again. Hard to believe iTunes log ins from years ago could screw up trying to share photos on my AppleTV in 2021.