My mouse pointer moves when I press the arrow keys on the keyboard

I'm not sure which crazy mode I've activated involuntarily on my Windows 10.

The arrow keys move the mouse pointer. Each time I press an arrow key, the mouse pointer moves into the corresponding direction by about 20 pixels.

I didn't find any setting neither in the mouse settings nor the keyboard settinsg that could trigger this behaviour. I'm also not aware of having installed any software that could trigger this.

Does anybody have an idea what this is and how I can get rid of this mode?

This might be happening due to MS-Paint being open. MS-Paint allows a user to operate the mouse cursor using the arrow keys. If MS-Paint is open, simply closing the program will result in this operation ending, however, if MS-Paint is not the cause, then you might have activated some function via shortcuts or function keys on your laptop. Check the search bar in your computers control panel for any such option (Mouse, Keyboard, Shortcut, Operation settings are good places to start). If neither of these solutions work, I would suggest using Google to look up specific functions of your PC/Laptop by entering the specific model number of the machine you are using.