I did not, by any chance, actually see any depiction of Chinese crossbow's pavises. Although I believe this kind of "shield" existed! Do anyone know about Chinese pavises?

do they even use them?
or it could just be a piece of wooden board sticking up on the ground.

These large shields were known as 櫓 or 卤 (both pronounced 'lu'). However, as far as I know there are no surviving depictions of them being used by crossbowmen.