If this desktop effect is what I think it is, I think I may have found some information to help (bit old information but could be still relevant)
If this is still true today, they might be some hard-coded defaults that kwin has.
This part of the post got me thinking that it might have a chance solving your issue:
“However, the up/down swipe gestures can be disabled by going into KDE Settings > Workspace Behavior > Desktop Effects and disabling Desktop Grid and Present Windows. The left/right gestures cannot be removed without disabling all virtual desktops.”
More of a work-around than a true fix, but hopefully that information is helpful still.