Mirror's computer input method is beneficial, but needs to treat other game controllers (Xbox Controller, Playstation Controller, and controllers like those) uniquely.
With all other non-crank analog controllers there is a problem;
When you let off the stick, it returns to center. This path is not a linear degree of rotation all the way down, which can jiggle input off of what the intended analog input would be with a Playdate.
Second, and more annoyingly, most controllers have a "flick" where returning the stick to zero overshoots the zero space, resulting in the opposite direction being sent, before returning to zero. Heavy use / weaker torqued controllers will have a more dramatic effect of this.
The Playdate Mirror should have a huge deadzone, such that input only matters when it is at the very outskirts of the input.
For those using Windows, if you open up the controllers/joysticks section of the Control Panel, click a controller and then 'Properties', for the controller I'm using now (PS5 Dualsense), rotating the right stick controls the 'Z Axis' and 'Z Rotation'. When centered, the two are at 50% each.
Playdate Mirror should only be accepting input when either Z Axis or Z Rotation is below 10% or above 90%.