Recently bought a used Switch 1 as people were getting rid of them to buy the new one, but I found out that mine came with an insane amount of drifting.

Opening it up was a pain in the ass and pretty scary, but I managed to fix it by putting a card over the metal plate on the left (to apply pressure under the joystick as many people online instructed)... And it worked!

It used to drift all the way to the left whenever I let go of the analog stick, but now it snaps firmly back to the center. Just wanted to put out a PSA that if your Joycon is drifting, it's very fixable. All you need is the right screwdriver and being very careful when lifting up each piece.