The Bug:
Block cracks are not affected by the fog from powder snow or lava.
Block cracks refer to the breaking animation that is displayed on a block while it is being destroyed.
Steps to Reproduce:
Enter a large area of powder snow or lava.
Switch into third person.
Begin breaking a block that is in front of you.
Take note as to whether or not block cracks are affected by the fog from powder snow or lava.
Observed Behavior:
Block cracks are not affected by the given fog.
Expected Behavior:
Block cracks would be affected by the given fog.
Can confirm for 1.16.5. (Only with lava of course.) When reproducing it with lava I recomment to use this command to prevent you from taking damage from the lava in survival mode: