I have had joycon drift in both sets of my joycons for at least a year. It actually made me switch to the pro controller full time.
But I watched a video on Nintendo Life (hello, loooovely peeeple), and now I'm cured.
You need to lift up the membrane underneath the joystick with tweezers or a paperclip, spray a very small amount of electronic cleaner in there, and rotate the stick for a full minute. Then let it dry for at least an hour. Make sure the controller is off and that you don't press any buttons whatsoever as sending electric current through the controller is the very last thing you'd want to do.
Both my neon and gray set are now perfectly fine and I haven't had the slightest bit of drift since.
How long has it been since then?
I'm opening up my Pro controller right now lol. Wanna get myself familiarized with this whole fixing/cleaning controllers thing, as it seems like a meta thing to do for as long as the Switch is around.
Not very long, to be honest. Maybe a month, and I'm not using them like I was when I was playing BotW or Mario Odyssey. In fact, I still use my Pro to play Rocket League because I trust it more. I really love the concept of the joycons, the same as I did with the Wii/nunchuck. It's a bummer that since day one we've had this problematic aspect of the design.