I also couldn't connect to my TP-Link Deco mesh system but that finally got solved with an update. At least to the extent that I could test it before setting this thing aside for other reasons. I may come back to it when I have a day to waste on it.
That's the Apple TV remote. When using the Harmony controlling the Apple TV over Bluetooth, it's possible to control the volume of the Apple TV itself, providing control of BT headphones via the handset.
The original remote not having a button is no reason to not have it available in the command set if the device supports it. Apple TV has several examples.
Oooh! I need that functionality too. I've set the SofaBaton aside for now because it's too much hassle. Will work on it this summer when I have a whole day to blow.
On my Harmony, I control the Apple TV by BT. I have the Volume control mapped to a sound bar and the Ch Up / Ch Dn controls mapped to the Apple TV to control the volume of AirPods Pro. Until the SofaBaton can match this, it's a nonstarter for me.
A few months ago, my Vizio got a firmware update that added a new feature. The ability to set what input the TV powers up to. That caused a bit of grief until I discovered it. Does yours have that setting? Related to that and SmartCast, I was never able to get the Vizio out of SmartCast from the Harmony directly. I could only doing it by cycling through inputs, which is far less than ideal.