Where are the contacts stored on the Contacts app?

I have solved that last question with a Google search.

I found the the way of accessing the User Library folder in the thread below.

https://discussions.apple.com/thread/8038868

Just in case that thread gets deleted, here are the instructions provided by Glen Leblanc.........

If you want to unhide and view the user library in the Finder view of a particular TM backup:

Navigate to the backup on the TM disk you wish to view. Select your Home Folder in the user folder of that backup. Right click on your account name (control Click) and then hold down the Option Key. Select copy "***" as Pathname.

Then, go the the Finder, select Go from the menu, then Go To Folder and paste the copied pathname to the window. Add   /Library   to the end of the pathname in the window, then hit Go. A Finder window show open that backup user Library folder.

Thanks Barney.

There is a further problem. As I am accessing the TimeMachine backup as though it is a normal series of computer folders I cannot get to the user Library which is hidden.

How can I do this as I drill into the TM folders.

Just in case you or anyone else is not clear how I am accessing the TM files and folders, the screenshot below should make things clear.

I forgot to reply to your last comments.

When I open Time Machine I get red bars denoting the backups but in this case they are all a slightly DULL RED and do not open (see arrowed screenshot).

The backup was made on Mojave and my iMac, as mentioned earlier, has been upgraded to Catalina with an erase and clean install.

Any idea why the backups don't work as they should?

Thanks Barney.

I am now wondering why the TimeMachine backup doesn't work normally.

Any idea why I am getting the dull red markers by the backups that don't work?

I have been plagued by this sort of thing for years.