To me, a MAGA Republican has always been someone who heard “Make America Great Again” and thought that “great” would mean things Republicans would support and provide, and that Trump would be a good President and would bring some sort of “greatness” to America. And, where what they tend to have in mind tends to include things like WASP culture, Fundamental Christian dogma, Puritanical tendencies, abolishing welfare programs and environmental protections, cowboy diplomacy, patriarchy and not having to hear complaints from women, no LGTBQ tolerance, abundant high-paying jobs for white people, non-white people and homeless and unemployed people going away or “staying in their place”, brutal police stomping out “crime”, unchecked capitalism and infinitely-increasing corporate profits, climate change denial, lots of military spending, machismo, solving school shootings by arming teachers, etc.
Oh, and yes, as @Demosthenes wrote, the kind of people who would hear “Make America Great Again” and think it needs no further explanation. And anyone who thinks it does need more explanation, might be someone who should leave or shut up.