Follow this process to disable touchscreen on Ubuntu.

Go to the terminal and type man xinput

It says that xinput is a utility to configure and test X input devices.

It has a lot of options but the one we are interested in is list

Then do this:

xinput --list

It will show you something like this:

Virtual core pointer                            id=2    [master pointer  (3)]
⎜   ↳ Virtual core XTEST pointer                id=4    [slave  pointer  (2)]
⎜   ↳ SynPS/2 Synaptics TouchPad                id=13   [slave  pointer  (2)]
⎜   ↳ Raydium Corporation Raydium Touch System  id=15   [slave  pointer  (2)]
⎣ Virtual core keyboard                         id=3    [master keyboard (2)]
    ↳ Virtual core XTEST keyboard               id=5    [slave  keyboard (3)]
    ↳ Power Button                              id=6    [slave  keyboard (3)]
    ↳ Video Bus                                 id=7    [slave  keyboard (3)]
    ↳ Video Bus                                 id=8    [slave  keyboard (3)]
    ↳ Sleep Button                              id=9    [slave  keyboard (3)]
    ↳ Integrated Camera                         id=11   [slave  keyboard (3)]
    ↳ AT Translated Set 2 keyboard              id=12   [slave  keyboard (3)]

Find the touchscreen system id and disable it.

I initially got confused between choosing Touchpad and Touch System.

I looked up Raydium Corporation and indeed they do touch screens.

In my case the id is 15

So I did this:

xinput disable 15

If you feel like you made a mistake and cannot live without the touchscreen then just do the opposite:

xinput enable 15

Using obviously the id that corresponds to your config.