Plants Cannot Generate or Be Placed on Snow Blocks

In the 1.18 experimental snapshots grass and ferns could generate on snow blocks, and other plants could also be placed on snow blocks.

This could no longer happen in the first 1.18 snapshot, 21w37a and later. Whether this feature was intentionally reverted or was forgotten to be ported to the snapshots is not mentioned in any changelog or other easily identifiable official source.