I see the watch is supposed to be able to connect to my InReach Explorer, but it doesn't seem to be working. I have the Explorer + model which I do not believe uses ANT+ connectivity, only bluetooth. Is this connection only supported on the new InReach Mini?
I think you're right, in only works with InReach Mini. The communication is done via ANT+. On Mini, there's a menu option to enable ANT+ and then you pair it as any other sensor. This will by default enable widget and add InReach screen to all activities (which is kind of annoying, I don't need InReach for road running). But if Explorer+ doesn't have ANT+, there would be no way to pair it.
I wonder if it would be possible older InReach devices will get ANT+ support with firmware update. Bluetooth and ANT usually use the same antenna and electronics, so one can always hope.