Airam

That's almost certainly a drifting analog stick on one of your connected gamepads — Windows treats the phantom stick input as cursor movement, which is why it creeps to the corner. Unplug your controllers one at a time to find the culprit. To confirm it (and see how bad the drift is), I built a free browser tool that shows your sticks' live positions: https://game-padtester.com/ — no install, just open it in Chrome or Edge and watch the stick dot. If a stick doesn't sit dead-center at rest, that's your drifter, and you can then bump up the deadzone in LaunchBox/Big Box or Windows to compensate.

Since the manual XML edit works for some people but not others, the difference may be whether BigBox is running when you edit the file — it rewrites InputBindings.xml on exit, so make sure BigBox is fully closed first, then double-check your edit is still there after launching it again. Also verify your stick registers as analog axes (not POV/digital) in Windows' 'Set up USB game controllers' calibration screen. If the axes move fine there but BigBox still won't map them, filing a bug report with your exact controller model is probably the fastest route, since this keeps coming up for multiple people.

Make sure RetroArch is fully closed and not just minimized — check Task Manager for a lingering retroarch.exe, since it can keep holding onto the controller. Also, if you run Steam alongside it, Steam's controller input layer sometimes fights RetroArch for the device; try disabling Steam Input or closing Steam entirely and see if the issue goes away.