How do I access the backed-up files on the external device?
MacBook Air 11″, macOS 10.15
Files backed up with Time Machine are not intended to be accessed directly. To use them, they must be restored. To learn how to do that, please read Restore items backed up with Time Machine on Mac - Apple Support.
You don't access them directly.
If it helps, do not open the Time Machine backup disk using the Finder. Do not even attempt to view its contents in that manner. It's not designed to work that way. Besides, the temptation to alter its contents is apparently an overwhelming and irresistible compulsion, judging by the number of Mac users who do that and thereby render their TM backups corrupt and unusable.
It is harmless to merely inspect a Time Machine backup device using the Finder, but do nothing else. Look but don't touch.
To learn how to restore individual items (files, folders, apps, etc) from a Time Machine backup, read the Apple Support document referenced above. To learn how to restore an entire system (everything, including all User Accounts and macOS itself) please read Recover all your files from a Time Machine backup.
Thanks for your assistance John. Much appreciated.
Thank you John.
I didn't know that about Time Machine (I've just started using it).
But I still don't understand how to access the back-ups from the external device.
You're welcome. Time Machine is a unique product. As a category of its own it's frequently misunderstood.
I backed-up my MacBook with an external device (Lacie USB 3.0 Drive) via Time Machine. When I try to access the apps on the external device a window appears "You can’t open the application “Photos” because it is in a Time Machine backup".
