xinput only works on Xorg, this is what x stands for. But Ubuntu 21.04 switched to Wayland by default. Wayland provides a new command that is libinput. There's nothing special. libinput's configuration interface is available to the caller only, not directly to the user. That means you should write some C code that will include libinput libraries and call the functions by yourself. Then source that file somehow. Shortly, you can't easily do the same things that xinput can do.
In our case, the caller, is the Ubuntu itself, who cares about input device configuration that is possible using gnome settings. Unfortunately, these settings are global for all devices, i.e if you change the mouse speed, it will apply to all connected devices that can impact the cursor, so the trackpoint speed will also change.
If you really want to disable that trackpint on Wayland, you can try using a udev rule like:
ACTION=="add|change", KERNEL=="event[0-9]*", ENV{ID_VENDOR_ID}=="054a", ENV{ID_MODEL_ID}=="466a", ENV{LIBINPUT_IGNORE_DEVICE}="1"
you can retrieve the ID_VENDOR_ID and ID_MODEL_ID values using command:
udevadm info /dev/input/eventN
where N is the device number to ignore that you can obtain using command:
sudo libinput list-devices
(read more about ignoring devices on Wayland https://wayland.freedesktop.org/libinput/doc/latest/device-configuration-via-udev.html#ignoring-devices)
or you can switch back to Xorg and do whatever you want until the community implements things properly.
