Leaving footprints - how would you do this?

It looks like the left and right foot can't be identified separately which would make realistic footprints quite difficult. https://developers.meta.com/horizon-worlds/reference/2.0.0/core_playerbodyparttype

If you can recognize left from right, you could potentially spawn a footprint asset from a pool at the alternating left/right positions whenever the player is touching the ground.

I could imagine this getting pretty complicated 🙂 You might, for example, track the height of the feet (once you identify them) and spawn a footprint every time they move up from a collision. Then you'd also start to worry about which direction the feet are facing.

An easier approach, depending on what you are going for, might be to leave a sort of wide trail in the ground. Or scuff marks and such trailing the player as opposed to clearly identifiable footprints. You could then have the asset spawn on the ground wherever the player is touching and then return to a pool over time. This could enable gameplay where you might be tracking other players. 

An even easier approah that might be in-line with what you are thinking would be to have a specific floor type that would receive footprints. Scattered somewhat sporatically as prefab assets. Think of this like mud puddles. Each mud puddle could have its own associated footprint assets. So if the player walks through a trigger associated with this "mud puddle", a child entity (showing vague mud markings) would simply be set to visible. In this case, you wouldn't get clear directional and accurate footprints but you'd know whether another player had gone through this way or not. 

I hope to see how this turns out for you.