I was surprised to see a "Gestures" program already installed and running at startup on Gnome 20 (freshly installed from 20.0.1).
But it was not working at first.
It took a while to research, but it was using https://github.com/bulletmark/libinput-gestures/blob/master/README.md as upstream lib package, right?
So after running
sudo gpasswd -a $USER input and rebooting it started working.
I think this needs to run on OOBE basis, right? How can I report this bug?
I hope it helps someone else to solve custom gestures not working.