I am unable to complete a Time Machine backup

I am unable to complete a TM backup because I repeatedly get "Failed to copy file" errors.

I looked at the discussion here: https://discussions.apple.com/thread/253012759

and tried all that, but it didn't help.

When I look at the log I see that many of the culprits are similar to this:

...Power Mac G4/2021-12-24-104431/Internal 1TB

SSD/System/Library/Templates/Data/Library/Application

Support/Apple/Photos/Print

Products/Themes/PhotoEssay-Large.pptheme/Contents/Resources/fi.lproj/TextStyles/HelveticaNeue.strings'to

'(null)', error: -36, srcErr: YES

2021-12-24 11:19:02  Mountpoint '/Volumes/Seagate 4TB'is still

valid

2021-12-24 11:19:02 

That is, they are in the Application Support folder for Photos. Since this is in the System folder I excluded the System folder and tried again. No luck. The same files failed to copy.

In addition, a few data files which are mysteriously located in the "untitled" partition of my hard drive failed to copy.

This is Catalina.

Can anyone help?

[Re-Titled by Moderator]