Gonna make you cough up a reliable citation on that one.
The kombucha folks don't seem to have a problem with vitamins of aseptic purees after processing and generally seem to have converged to aseptic as being superior in terms of nutritional content than any other mechanism including freezing and preservatives. And Vitamin C is notoriously fragile to heat. Generally, Vitamin C is far more fragile than anything in milk (standard pasteurization knocks down Vitamin C by about 50%!).
Overall, though, the nutritional content is "mostly" unaffected by UHT. B1 and B12 drop roughly 10-20% for both types of pasteurization.
The primary issues with UHT are Lysine and folate. Lysine gets clobbered by the Maillard reactions. The folate you cited is definitely a concern given that folate and Vitamin D are factors in preventing birth defects.
And, you are correct that the taste does change since UHT kicks off Maillard reactions in UHT milk. TIL.
However, we come back to the fact that "standard" HTST pasteurization changes are so minimal that the risks of raw milk FAR outweigh any possible gains therefrom.
And if you don't have a reliable cold chain, UHT pasteurization is pretty good with caveats.
Taste is significant though. My kids (spoiled brats) refuse to drink UHT and they recognize it immediately
Pasteurization is heating to 70C and cooling it down quickly to kill pathogens. The milk needs to be refrigerated afterwards and used within 2 weeks.
UHT is heating it to 140C for 2s a cooling it to kill pathogens and their spores. It significantly changes flavor, destroys 90% of vitamins and changes some of the proteins structure. Lasts a year afterwards