I have disabled all gnome extensions with Gnome Tweak Tool by clicking on the switch that appear on top of all extensions list to disable all of them in one click.
Now everything is disabled and the switch on top is also disappeared.
I tried rebooting but the tweak tool still does not allow to re enable any extensions anymore:
I also tried with https://extensions.gnome.org/local/ but even re enabling them manually (clicking on the on/off switch) works. The switch shows "on" but the extension is not actually enabled. Reloading the page shows all off.
Best Answer
...ok I have found how to solve it.
It looks like that tweak tool has a bug...