MXGP 2021 - The Official Motocross Videogame (UP)

To perform a scrub you need to pull the anologue sticks in opposite directions at the same time. This results in you bike going on its side (and then also flipping all over the place if you hold it for too long). From my testing you don't even need to successfully land it, so head on over to the playground and experiment with together until something desirable happens