Thanks Mathias, I guessed it was probably Win10 & not MC.
I am the only user, my a/c is the passworded <name>/admin a/c. I have not allowed any other guest etc a/c's.
Booting without password doesn't give me/anyone full access.
'Users' group has zero permissions.
So I have full permissions, but programs installed & run by me in this single environment might not....
Not logical or helpful.
In the example of Handbrake & MC (both running in an admin environment but not admin mode) I can load a file using the 'open source' (browse) dialog, but not drag n drop. Only possible when MC is in Admin mode.
I think M$ needs to streamline this muddled, contradictory & illogical behavior.
Full admin control is potentially dangerous but as sole user that should be my call.
Anyway I will keep poking about & see if there is some buried switch that I can use to improve this situation.