Hello @Federico Coppola ,
Thank you for posting here.
Based on the description, you configured the following two GPO settings.
Computer Configuration > Policies > Administrative Templates > System > System Restore > Turn off System Restore => Disabled
Computer Configuration > Policies > Administrative Templates > System/System Restore > Windows Components > Windows Defender > Scan > Create system restore point => Enabled
And you enable and configure System Restore for all Windows 10 Professional, is ti right?
If so, I am so happy that you get the requirement you want.
Meanwhile, you want to set max disk usage on all the Windows 10 Professional, based on my research, we can set max disk usage on PC one by one instead of GPO.
Hope the information above is helpful.
Should you have any question or concern, please feel free to let us know.
Best Regards,
Daisy Zhou