Backup to Time Machine
I was notified two days ago that there had been no backup for 18 days. In System Preferences, Time Machine shows 259 GB of 1 TB available, and Preparing backup. . . Back Up Automatically is ticked. Screen says: 'The oldest backups are deleted when your disk becomes full'. Options shows Estimated size of full backup 123.56 GB.
It looks as if the disk is nearly full. Finder shows the last backup as 2023-07-31-212217. The oldest files are dated 2016. I deleted the six oldest files and machine has been off and on again since then, but still no backup.
Machine is old (late 2013). MacOS Catalina, Version 10.15.7, with no updates available.
Mac Helpdesk was about the least helpful I've ever known on this.
Any ideas?
iMac 21.5″, macOS 10.15