move the instance collection to the point of contact with the plane?

Question

the task is to move the collection of instances to touch the plane with the bottom point

Answer 1

To do this, you would only have to send a raycast down to the plane.

Note that the center of the object is always the source of the raycast, so you have to compensate this additional distance with the offset.

Answer 2

You can simulate¹ falling down² by raycasting down like in quellenform's answer, but then taking the lowest ray for each group (not island, because one Suzanne is 3 islands), and displacing by that much…

An Animated Plane as a Base:

The Snapping Action:

A Demo:

¹ - not a simulation zone, "simulating" means "pretending"

² - well, not the process, just the end result