Time Machine backup fails

Jan Becket wrote:

Erase and start over?

I have waited overnight and the terminal command tells me Filevault is on - no problems. The TM backup message remains the same - backup not completed. Is there an error log that can be viewed?

Sure why not, I would erase/reformat/initialize the parent drive as new your external drive

ref: Erase and reformat a storage device in Disk Utility on Mac - Apple Support

Verify you format as GUID/APFS. Disk Utility>View>Show All Devices

Jan Becket wrote:

I set up a new Time Machine disk but after the initial backup, I get a message that the TM backups cannot be completed. The details state that "anti-virus software may be preventing Time Machine from writing to the backup.” Pretty vague. I deleted Malware Bytes from my computer. Same message. When I right-click on the new Time Machine disk, it says that it is encrypting, but it has said that for the past two days. Why would it take over two days to encrypt a disc? Another message on this forum suggested that I need to turn on FileVault, and so I did that. No difference. Erase and start over?

If you turned on FileVault you will need to wait until it completes. Then try again your TM

You can see status from the Terminal.app copy & paste:

fdesetup status

or from the >System Settings>Privacy & Security