It’s a well-known drawback of Plasma Wayland session, you cannot disable these built-in gestures until they add the respective config option. I believe there’s plenty of bug reports on this, just too lazy to look them up. In brief, you need to “thank” KDE devs for this questionable decision…
PS: I guess even Plasma 6 won’t have a switch-off for it – at least I haven’t seen them planning this.