@petr. OK noted. I have a working Rescue Disk right now, so may be some time before I try and create another.
Edit:
Avast Free AV 20.6.2420 (build 20.6.5495.588)
I have today been able to create a Rescue Disk (USB), without first turning shields off.
Also Rescue Disk USB boots, and the 3 functions tested OK.
However,
On clicking Restart prompt from Rescue Disk, Windows 10 starts but Avast tray icon is ineffective i.e. does not obey left or right clicks, long after it appears. I have done another Restart and avast tray icon again is dumb for well over 1 min after it appears. I may do a APP REPAIR to see if any improvement, else will post separately as this is a different issue from Rescue Disk.