The New feature Clear All Slicers button (part of March 2023 release) works only for the 1st time in both desktop & Service. And it does nothing when you do some more slicer changes & try to use it 2nd time. When you click, it does nothing! It is of no use if this issue is not fixed.
Once “Single select” is turned on, the user must always have one default value selected in the slicer – you cannot have no values selected in the slicer, so the clear all slicers button cannot be used in single select.