I believe that this is by design for those default scans where you can not change the what to “Scan”.

I am not sure why someone would want to change the “Scan” settings on these scans

If you want to crate your own what you would consider a full system scan then go to “Settings”----“Basic”–and click the box under “Special Scans”. Then go into “Scan Computer” and at the bottom right click on “Create Custom Scan”. Then you can create a scan to scan whatever you like.