If you use KDE with wayland, then :

• You can switch desktops horizontally with three or four fingers
• You can only switch desktops vertically with three fingers
• By default, four fingers vertical opens present windows or something like that

To be able to use four fingers swipe up, you need to disable present windows first. Go to settings > workspace behaviour > desktop effects and unclick desktop grid and present windows (in the hope that you have no use for them)

Then you need to install evemu and libinput-gestures (if you're on Arch, it's in the pacman repo and the AUR respectively)

Once you have it installed, run in your terminal evemu-record. It will list all of your devices. Shut down the program with Ctrl + C and look at the event for your keyboard. Once this is done note it down.

Create a new file

nano sendkey.sh

Copy the content of this code in the new file but replace EVDEVICE=/dev/input/event4 with your keyboard.

#!/bin/bash
# sendkey.sh

EVDEVICE=/dev/input/event4

for key in $@; do
    evemu-event $EVDEVICE --type EV_KEY --code KEY_$key --value 1 --sync
done


# reverse order
for key in $@; do
    evemu-event $EVDEVICE --type EV_KEY --code KEY_$key --value 0 --sync
done

Ctrl +O then CTRL + X to save then quit nano. Once it is done run this command : chmod +x sendkey.sh then open the gestures app and start mapping away. The interface is very intuitive. What you want to do is click on the little + at the top bar then select the motion you want to bind (in your case swipe + up + 4 fingers) and in the command at the bottom you write /home/YOURUSERNAME/sendkey.sh LEFTMETA W

And there it is. You can map pretty any keybind to any event with this. Hope this helps.