After upgrade to Plasma 5.21.5, no more touchpad/trackpad settings in System Settings>Hardware>Input Devices.

On X and Wayland.

Touchpad/trackpad settings changed to default from libinput

Thanks for reporting, fixed in plasma-desktop 5.21.5-2 (latest libdrm change, required new makedepend for plasma-desktop).

I confirm, it works now.

Thanks.