i don't think the weapons is that B&T VP9.
https://x.com/CollinRugg/status/1864376425685438810if you slo-mo the video, down to 0.25x speed, blow it up to full-screen (monitor on a desk-top, forget looking at it on a dinky little mobile phone screen), for the first shot, you can clearly see the slide cycling. conventional semi-auto like.
also, from how the shooter manipulates the slide to clear the malfunction, he grasps the slide normal-like, and pulls it straight back. also, when he has to tap it into battery, that's also something for normal semi-auto pistol. Also, from the grainy video, doesn't look like a hammer-fired pistol, so, striker-fired.
looks like it failed to eject on the first shot, so he clears the malfunction and takes a second shot.. malfunctions again, he's clearing the malfunction while walking up to the victim to take the next shot. From the 2nd shot onwards, it's too grainy to make anything out, also, no audio.
could be one of those common 9-mills, after all, he traveled from-or-through Atlanta on his way to NYC.
but I'm no expert.
also, video shows the backpack as gray, however, the backpack found in the park was blue. Could be the lighting from the flashlight. Tactical flashlight, cough, excuse me. The sidewalk shooting security video is in color, and doesn't show the backpack to be blue.

time will tell, we shall see. OTOH, it being the Eff Bee Eye, maybe we'll never know.