which will not let me exit after selecting "Off" in the Select thermostat mode dropdown (which doesn't acknowledge the "Off" transition. It seems that I can move on to the next screen to complete the If/Then only if I set a heating point as noted above.
Not sure, I can do that with all my thermostats. I have 4, three are using a virtual thermostat app, VThermostat and the 4th is an Ecobee. using the Ecobee suite manager from sandood,
It looks like you are trying to edit a broken action. Is that the case?
It may mean the rule has got corrupted.
If this is all you have in the rule then maybe try deleting and starting again.
Thermostat driver is the Generic Z-Wave Plus Thermostat driver. Regarding the broken rule, I think that came about when I couldn't set the thermostat to "Off" and then tried setting the temp to "70" which was accepted and allowed me to continue the If/Then. I then tried to back up and apparently broke the rule. Deleted rule and tried again but still got hung up when trying to select "Off" in the "Select Thermostat mode" dropdown. Nothing apparent to select that allowed me to move on to complete the rule. Very strange.