why don’t you use slider for this ?
If you still want progress bar then the easy way is you can put slider over a progress bar and sync their value, and hide all slider background, the you can have your cap.
Tips: make an overlay, put both of them in, make sure you have the slider is put there after progress bar, slider will be on top of progress bar, then both in Slot choose horizontal and vertical fill, Now you have overlay as a custom progress bar with cap, can make a widget an reuse everywhere.