I need help with whatever trick this is called

That is a foot jam whip, try finding your balance point when jamming your foot and work your way from there.

It is a footjam whip or whiplash.

You need to be leaning more over your bars, so your chest is over the bars. This will let you stay balanced in the footjam.

It’s a pretty fine margin between just right and too far forward coz you still need the whip to come around without the back wheel hitting the ground, so there’s less room to move your body to balance than any other footjam variation. But the back wheel will generally only be a few centimetres off the ground while it comes around.