Has anyone mentioned what happens to the jitterbug or the Charleston and 1920s flapper culture in general OTL?
Swing dancer here. I know some of the history so I'll give this a shot.
What I'd imagine would happen to it, much like what I'd imagine what would happen to jazz, is that it'd have a connotation of survival that it doesn't have in our timeline. It becomes hallowed.
There would be far less appreciation of black dance and music by white people, partially because of the border between the two countries preventing much of the OTL Great Migration and as such the loss of the New York scene and the Savoy Ballroom would put a stop to the racial integration that certain scenes became known for.
You do have the antecedents to Blues Dance in the South already; due to the sanctification I mentioned earlier it might not become the rather raunchy dance it's become in OTL, but it's said that southern Blacks were more prudish than southern Whites, so it could still move in that direction. A TL-191 Swing Kids might revolve around one of these blues dancing communities.
Interestingly, this world has no American possession of Cuba so Cuban dances wouldn't make their way to New York, leading to their transformation by Arthur Murray into their American forms (still danced today) and their grouping with waltz, east coast swing, and a few others to form what we call 'ballroom dance.' In particular you wouldn't see the transformation of the urban black Lindy Hop (a descendant of Charleston, and which in TL-191 would have a different name) into East Coast Swing, designed to be easily teachable and more palatable to middle-class whites.