Ok... I can't believe it... I installed Acronis True Image 2021 (the Trial) and after the reboot the System Restore is now working... I was afraid to try this "route" since I was afraid to getting things worse...
Now... What I can do to recreate the problem if I uninstall this ..... software? Sure I will not use the AcronisCleaner (and I'll never use this software anymore) but I'm really afraid to uninstall and maybe not to fix again with a re-installation, maybe I can monitor the uninstallation by using an uninstaller program (like Revo Uninstaller and such)... I'll try if all is ok tomorrow before doing something.