No Sounds when toggle rhythmic slash notation

Indeed by design

Rhythmic slash notation is not supposed to produce any sound, not by default at least, all these slashes are on the same line, so no way to change their pitch, it doesn't even show the pitch in the status bar.

But switching on the 'Play' property will make them sound. At least the one (seemingly random) note of every chord, the others get lost in transit it seems

I use rhythmic slashes like [A].
This is a substitute for [B].
Therefore I want it to sound as a chord when playing.

Or, I would be glad if you could create a notehead for this feature.
For example, like the following image.

As soon as you toggle to rhythmic notation, all notes are turned into slashes and on the same line, all but one are turned invisible. So if you select it, to switch on play, you only get one of them, with no good way to get to the others.

You could select the slash and use element offset to moe it slightly, select again, move again... until you see them all, then switch playback on for all and reset their positions again.
Or (make a range selection,) right click one of the slashes, Select > All similar (in selection or staff), then reset the play property (i.e. set it to on for all)

Making this possible in a more direct way indeed is a feature request worth thinking about

The reason play in unchecked by default is that most people would not be taking the trouble to enter actual chord voicings for this - they enter "dummy" notes. So what you are doing is quite unusual. I think the method of making the ranges selection and then limiting it to just notes (you can also simply press the Notes button in the Inspector) should be sufficient as a way to accomplish that task.

Thank you for the advice.