The only app I know with which you can disable those dashes is
Windhawk.
That is software to modify the taskbar (and many other Windows 11 UI things).
It is a rather huge packet: it takes about 600-700MBytes on your system drive for just a few UI-modifications.
But it is very flexible, if you understand it's 'language'.
About two month ago I tested it and got very neat results with it, but decided not to use it (I have a licence for Start11 v2).
The dashes can be removed in the mod 'Taskbar Styler'.
With the command:
Target: taskbar:TaskListLabeledButtonPanel@RunningIndicatorStates > Rectangle#RunningIndicator
Styles: Height=0
So if you have some test-environment like Windows on VirtualBox or a separate test-PC, you could try to use that package to tweak the taskbar UI to your wishes.
A little list of all settings I made in Windhawk is included in the attached text file.
It does not pretend to be absolutely correct and maybe the used words here and there are incorrect (I originally made the notes in the list in Dutch language). I am not able to check it with the last version of Windhawk (if there is a newer version after end of April 2024), because I don't have it installed anywhere anymore on my systems.
Windhawk is a fully free package!