Although "automatic reverse geocoding" can be activated or disabled in the map panel (preferences menu), it would far easier to have a button in the map panel for switching the automatic reverse geocoding on/off.
See my response to your last request. The Map panel toolbar is already quite large on small screens, adding more buttons is probably not an option.
Another question is, how often do users need to enable/dsiable reverse geo-coding? I enabled it once and never looked back...