Try these checks in order:
- Close all open apps. If the mouse behavior improves, too many open apps may be interfering with input responsiveness.
- Check the mouse power and battery. If the mouse is wireless or Bluetooth, low battery can cause erratic behavior. Replace or recharge the batteries if needed.
- Restart the PC. This refreshes drivers and can clear temporary input problems.
- If the mouse is USB-connected, unplug it, wait a moment, and plug it back in. Also try a different USB port. If a USB hub is being used, connect the mouse directly to the laptop instead.
- Check the hardware. Make sure the mouse cable is not damaged, the sensor is clean, and there is no dirt blocking buttons or sensors.
- Test the mouse on another PC. If the same behavior happens there, the mouse may need to be replaced.
- If using a wireless receiver, reconnect it. Unplug the USB wireless receiver, wait about 10 seconds, then plug it back in.
- Update Windows. Go to Start > Settings > Update & Security > Windows Update and install available updates.
- Adjust mouse settings. Go to Start > Settings > Devices > Mouse > Additional mouse options > Pointer Options and review pointer behavior settings.
Since the touchscreen has already been disabled and an external keyboard is already in use, the most relevant next checks are the mouse itself, its battery or receiver, the USB port, and testing the mouse on another PC.
References: