The particle direction fix of MC-260093 has a bug: it checks for the brush being in the offhand, but not the left and right hands being flipped by the left hand option. As a result, when the player is left-handed, the brush particles will move left in the left hand and right in the right hand.
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Not a duplicate of MC-260093, that one concerned the particles moving the wrong way when held in the offhand, this one concerns the particles moving the wrong way when the main hand is set to the left. Similar, but distinct, issues.
dupe of MC-260093, if the "fixed" bug isn't fix, you can just comment on that "fixed" bug report rather than create a new bug report