I've been servicing controllers for at least 25 years now. The new analog sticks they put in now are terrible. Particularly because they're not actually analog anymore. Any dirt they pick up blocks the digital contacts and stops them from registering the stick position. That dirt gets pushed to the edges of the stick range and you end up with an outer dead zone.

WD-40 makes an electrical contact cleaner that works excellent when my Oculus controller starts drifting. Don't even need to take it apart. Just pull the battery, spray and roll the stick around, and let it dry. It'll be like brand new. Totally saved me from having to ship it back to the company. For Switch controllers or any controller with a battery that's not easily removed and can't be completely shut off, you'd need to actually take it apart to clean. I've seen guys do it without removing the battery, but you risk shorting them. Only one I'd be scared of is the PS5 controller. I've seen the breakdown on them and there's a lot to damage accidentally in it. Otherwise, most controller breakdowns are pretty easy and can be found on youtube. Just takes the right tools, which you can get on Amazon for like $10.