The bug
Experience orbs are no longer affected by the fog from powder snow/lava.
How to reproduce
Throw some Bottles of Enchanting inside a large area of powder snow/lava
→ ❌ Notice how you can clearly see the experiences orbs
Note: This is quite difficult to reproduce with lava as the experience orbs are almost instantly burned and destroyed, but it can still be seen for a split second. This did not happen in 21w08b.
This also happens with Fabulous!