After a bunch of comments pointing out to the fact that my GNOME touch issues were linked to Ubuntu, I did another try, on Fedora, this time, and yeah, it's MUCH better.

I also gave a shot to Plasma Mobile (excellent), and Phosh (less excellent on a big screen):

https://www.youtube.com/watch?v=nCSs4CbxZHk

I was WRONG about Linux & touchscreens: GNOME, Plasma Mobile and Phosh tested

YouTube

@thelinuxEXP just a nitpick: phosh is not: "some kind of fork of gnome shell."
Its a wayland and gtk shell that does use gnome technologies, sure. but was built from ground up. It does not have code in common with gnome shell itself.

Also there is another keyboard that can used with phosh that is better for tablets.

https://phosh.mobi/posts/phosh-osk-interface/

Phosh's On Screen Keyboard Interface

One of the central pieces on small screens without physical keyboards it the on screen keyboard (OSK). Ever so often people want to experiment with alternative keyboards to e.g. explore alternative ways of text input (via speech or swipe) or look into how to support languages and scripts that aren’t supported by default. An alternative on screen keyboard in Phosh Requirements Link to heading Due to Phosh’s modular design (the on screen keyboard runs in a separate process) exchanging the OSK is simple.

Phosh