Hi John, if the Apple TV is finding them on the network, than they’re AirPlay 2 capable speakers. The Sonos speakers that can’t use AirPlay wouldn’t even show up there.
If it’s failing to connect, I’d be looking at network connections or some settings that could be getting in the way.
Do you have an iPhone? If so, are you able to use AirPlay 2 to play to those speakers from it? That would let you know if AirPlay 2 works fine on the network, and then you can narrow things down to what’s getting in between the Apple TV and your Sonos speakers.
This page here has all the AirPlay needed steps for Sonos, which you’re probably already doing, but it’s worth a read.