It's all about mashing. I measured my mash and it tends to be between 9 and 12 left presses per second. It sucks and it tires you out really quick.

When I'm about to do the glitch, I usually turn my controller 90 degrees so the left button is the closest thing to my body, rest the controller on my leg, hold right (which is now away from my body) on the stick with my left hand, and mash like crazy with my right hand.

This is just a problem with having a glitch that was a little challenging at 30fps be ported to 60fps.

I hold my controller against the table for stability, that helps alot for me. But like Tina said, just mash fast!

I was having serious difficulties with it (going way too far to the right) until tina suggested that I left off the button more quickly after pressing it. After I understood this I got it pretty much immediately after.

It's very beneficial to have your directional inputs bound to buttons to be able to do the mashing properly, imo.

Question: does this work on switch?

Yes, Tina plays on switch and can do the glitch using a pro controller. Not sure about with joycons though.