@lonely-night yes, I also looked at that bts rear view of the festival performance and went "oh, high heels not boots!" too.
And then I thought I'd worked that out once before, when I was making a list of the contents of Kitty's black plastic bags. But you can't really make it out from the show, you barely see Kitty's feet on stage at a distance
So to the PR material. The staged photos come in two sets - their working clothes, and the final concert clothes.
Not that much difference between them for Kitty, but she's definitely wearing the tall boots in her every day clothes.
The absolutely highest quality version of the pic on the right that I can find (thank you TVNZ) shows that for her performance costume she's wearing really very blingy high heel ankle boots.
But that's not what she's wearing on stage. I don't think we saw those on screen.
To be sure I went back through other BTS stuff, which I had failed to save at the time (fail!). Thank you, Chandeep!
I'm pretty certain what she is wearing onstage is the studded high heels she wore when she met Beth at karaoke, studs/crystals around the heel and top of the front of the shoes, but not on the rest of the foot.