can confirm this in 1.21.5 pre-release 3, this also affects hay bales as well. feels like this was a result of lowering volume of breaking sounds for grass + other plants but it led to other blocks being affected that shouldn’t have (grass and hay bales)
Ah you're right, for some reason it didn't seem to be working but I realized I was only trying it in creative mode. Survival mode behavior works as intended, so you can consider this resolved.
to clarify i meant grass blocks when referring to blocks, and short grass when referring to the plant.
additionally, firefly bushes seem disproportionately loud when compared to other plants, although that could probably be classified as a separate issue.