Windows 10: Cursor switching to one with mini scroll bar (seemingly randomly)

If it doesn't arrive in Safe mode or Safe mode with Network, then this might be caused by some installed program or third-party device driver.

You might try first to update all drivers, especially mouse and touchpad, from the manufacturer's site.

If this does not help, to further locate the problematic application, you may use the free tool Autoruns for Windows.

This utility shows all programs configured to run during system bootup or login in its "Everything" tab. You may turn off startup items with a click and return them later with another click. You may avoid listing Microsoft products by using the menu Options > Hide Microsoft Entries, Hide Empty Locations and Hide Windows Entries

I would suggest turning off startup entries in bunches, drilling down to the startup program that causes this behavior. Once identified, it might have some setting that can avoid the problem, or can be left out of startup and only be invoked when required (verify that once invoked it does not add another startup entry, but such can again be disabled by Autoruns).

To short-circuit the process, start with products that relate to the mouse and touchpad.