Occasionally MacroDroid's Airplane Mode action (which I rely on all the time -- every time I get home MacroDroid turns it on, to force my phone to use wifi calling) stops working, for reasons I don't understand. But I can get it to work again by changing the Default Digital Assistant to off (or another application), backing out of that settings screen (just to be sure the change got recorded), waiting a minute, then going back and resetting it to MacroDroid.
I see that you rebooted your phone without getting the action to work, and rebooting should have done something similar to turning the assistant off and on, so this suggestion probably won't work, but ... you might try switching the assistant off and on once or twice to see if you can get the Airplane Mode action to work.
(FYI: The "airplane_mode_toggleable_radios" setting is as you suspected -- it controls the radios that can be manually turned back on even after airplane mode is activated)
(FYI #2: The Airplane Mode action does work fine even when the screen is off)