Turn On or Off Automatically Hide Scroll Bars in Windows 10 UWP Apps  

HOW can have a thumb (slider) in my scrollbar in a permanent middle or darker grey without hoovering ? that is my question in the end.

I apologize for the detour I had to make to come to an understanding what exactly caused my problem.
The final quarion is :
HOW can have a slider (thumb) in my scrollbar that shows itself permanent (middle grey or darker grey) without hoovering

I want to have the visibility of the slider as it is on hoovering, but then without hoovering.
Simply a permanet visible slider as it was for decades before MS decided that it is funny to hide the slider and make the people search for it.
In Firefox I have now installed a workaround by adding a stylesheet with the following code:
/* Higher Contrast Scroll Bar Thumb */
html, body {
/* thumb-color track-color */
scrollbar-color: #888 #eee;
}

Thanks to jscher2000 on Mozilla Support. It works fine on this site too.