If you have an item entity between you and a block you are trying to brush, the game won't let you brush it. However, the vast majority of other both left and right click actions are still allowed through items, which makes me quite sure this is not intended.

Steps to reproduce

1. Place suspicious gravel
2. Throw random stuff on the ground in front of the suspicious gravel
3. Fill up your inventory with brushes so you don't pick up the items
4. Go in survival mode (again so you don't pick up the stuff)
5.  Try to brush the suspicious gravel through the dropped items (it actually doesn't need to be a brushable block, but suspicious gravel is a good indicator for this example)

Observed result

it won't let you because the item is in the way.

Expected result

the item being in the way does not interfere with your ability to brush blocks

6. Hit the block

it lets you hit the block through the item, which means items are ignored in most operations

Interestingly, the area it doesn't let you brush is a lot bigger than the actual size of the item's hitbox.

This is most likely caused by the fix of MC-260898.