> Folk dances, however, were a whole thing with Stalinists (“culture that is national in form, and socialist in content”), so an outright ban would seem out of character.

Folk dances and culture in general were a whole thing with Stalinists, but authorities exerted a considerable degree of influence and a ban on some specific folk dances (or cultural manifestations), or on some specific aspects of them, wouldn't have been out of character at all.

Where I'm from, a whole range of folk dances, songs and theatre were banned not by name but under either a ban of the religious denominations that prominently practiced them or a blanket ban on public celebration of major Christian holidays, especially Christmas and Easter.

Folks dances, too, are kind of murky in this area. Perhaps one of the most widely-displayed folk dances of the Eastern Bloc in the communist era, a Romanian dance called "Căluș", retained some of its essential choreography, but was otherwise radically changed to drop its religious undertone, to the point where it was pretty much a different thing by the end of the sixties. Some of it was "recovered" in the eighties, when a peculiar for of protochronism began to permeate some official circles so doing the ancestors thing was cool again, but during the high Stalinist period the "old form" fell under a general repression of what was officially termed "religious mysticism". This led to an entirely peculiar situation where the dance was technically okay, kids learned something resembling it in school and danced it during official ceremonies at the city hall, but grown-ass adults who'd learned it from their parents (edit: not literally from their parents, the way it was taught was a whole thing and didn't help with the whole mysticism issue but anyway) and practised it outside official cultural institutions got rounded up.