When hovering over the button, no tooltip appears.
When clicking the button no tooltip appears.
When dragging the button the tooltip appears showing the current value, but after dragging the button and releasing the mousebutton nothing has happened.
Clicking somewhere on the slidebar will change the value, but you can only set it to a preferred value by some trial and error.
Here’s a video showing what it looks like on my system:
https://youtu.be/84BGD12Cm_I