Simplest solution I know of is to use fn lock. Press fn + esc, that should do the trick. same to undo it.
Read this comment on brightness hotkeys
Not sure why others hotkeys are not working, maybe wrong keyboard layouts is selected?
I’m also on KDE Plasma, mine is selected to Generic 104-key PC. I am using a British English Keyboard if that matters.
Hopefully someone else can chime in about this.
I know Wayland has support for gestures in KDE. Double check the touchpad setting just to be sure. I do have tap-to-click enabled, rest was as is. I can use pinch to zoom in and out.
Hope this helps.