Not sure if it's okay to ask for support in here, I'm just giving it a try. 🙂
I'm using Manjaro Linux with KDE 5.26, and I thought in this release touchpad gestures should be working out of the box, but I was wrong. In an X11 session, I got three-finger swipe up/down to switch virtual desktops, and in Wayland I just get two fingers for scrolling, everything else doesn't seem to work.
Turns out a Wayland session isn't working for me in a number of ways (for isntance, the keyboard isn't even working right).
In X11, the only thing that works is two fingers to vertical scroll
Touche should be installed and configured for X11 sessions. For Wayland I'm not sure but did assume they were working. You can try touchpad settings perhaps?