Hi sotos mad,
Thank you for sharing the video information here. Although I didn't see the mouse in the video, I can probably understand your question.
When you hover over the slider, the volume slider automatically moves to the left, right? Similarly, similar "automation" operations also appear in the calendar, resource manager.
From the video, it looks as if the computer received a command that caused the slider to move.
I recommend trying a clean boot which starts Windows with a minimal set of drivers and startup programs. It can be used to determine whether a background service or program is interfering or causing a problem.
These steps of "clean boot" might look complicated at first glance. However, to avoid any trouble for you, please follow them in order and step-by-step.
After the "clean boot" is done, check whether the same problem occurs when you hover the mouse cursor over the slider again.
If the problem does not occur at this time, the problem should be caused by a process on the system that you have temporarily disabled because of clean boot.
Therefore, refer to the following steps in the link to troubleshoot the disabled processes according to the instructions:
.
However, if the problem persists, hover the mouse over the slider and remove any input devices connected to the device at this time, including the mouse, keyboard, and controller. After removing all input devices completely, verify that the problem persists.
Best regards,
Mitchell - | Microsoft community support expert from MSFT