So I searched up this as requested and found something similar that had been reported a long while ago. However, it was marked as resolved because of invalidity. This turns out to not be the case. After testing in both the latest snapshot (21w42a) and the latest release (1.17.1), I've found that the particle animation for the sword swipe still plays from right to left no matter which hand is set as main by the player. I have tested this both with and without mods (primarily Fabric Loader, OptiFine, OptiFabric, Mini-HUD, Litematica, Malilib and Replay Mod) and the results stay the same.