It is like this (see below). The 'Name' at the top shows it is a simply copy of an existing one. As said I merely changed the Dual Vertical display, only to see how it would look like.
In the 'original' one, when editing style > Right File Display > Format: Edit > tab: Hide Filters it shows:
File names: *.(ini|db|xml|xmp)
Folder names: *
This is also in the dual display version, both on the left and the right
BUT.... I let it rest, getting unexpected effects anyway, like, in case of 'Show files only' thumbnails left, details listing left. Not worth spending more time on this. Deleting this style.
That explains why it's hiding things. If you don't want it to hide all folders, remove the * wildcard from the Hide Filters / Folder Names field.
The original should also be hiding them if it's set to hide * folders. So the only potential mystery here is why the original isn't acting the same way.
Sorry for the delay.
I believe I have found the reason:
The original style (from which I made a copy), Edit, Left... file display, Format, Hide Filters, there was no * in the Folder Names box.
So, folders were displayed, rightfully so.
Indeed, the strange thing is that after copying and merely changing to Dual Vertical to see what would happen/what I would get, one way or the other a * seems to have beed added to the left file display.
Mistery solved