The Joycon's control stick

So about the broken Joycons, I realised that the only problem is that the joystick in one of my Joycons doesn't work as intended: when I point it somewhere, it doesn't stop going that way. And it's not the distance between it and the dock. Because even in handheld mode it happens. What's the problem?

You should try recalibrating the control stick. Do that first. If if bad even after that, it's probably something wrong in the hardware.