In my world of harmonica reeds, torsional vibrations is not a thing.
SQUEAL!
Sure, torsional vibrating is a great explanation for what makes a harp squeal when someone is struggling to play overbends or even regular draw and blow bends. Instead of just moving up and down, the reed also wiggles from side to side.
But torsional vibrations is just another word for squealing and squealing happens because the reed doesn't close the slot properly. It's really as simple as that. There isn't a special kind of squealing or a library of specific remedies to address a vast array of different squeals.
Harmonica reeds squeal because they don't close the slot properly.
Reed work (and obligatory Framework) should fix that. Make the slot straight and then make the whole length of the reed pass through the slot all at the same time.
Some harps are more prone to squealing than others. Why is that? It's still because their reeds don't close the slot properly.
Addressing the issue with wax or other foreign substances is not optimal because it changes the timbre and response and lowers the available range. It can add variability to the pitch and the reed tuning will drift.
Will embossing help? No. Not in of itself.
I hope that helps.