Operation Can't be Completed Because Backup Items Can't be Modified (Not a Time Machine Volume)

Mac OS does not require nor does it benefit from adding third party antivirus. The best antivirus app for Mac OS is Mac OS itself. By introducing third party AV apps you will only make Mac OS slow, unstable and appear to be buggy. Please locate the developers instructions to uninstall BitDefender and follow them to the letter.

In order to keep Mac OS secure, simply keep Mac OS up to date.

BTW, the same holds true for "cleaning" apps or any other types of third party "maintenance" apps for Mac OS, almost 100% of them are complete garbage and only serve to take money out of you pocket and offer no benefits in return.

What "Operation" are you referring to?

What are you using to look for and delete Malware?

Most all third party AVware, Cleaning Apps and Malware removers are bad news and may cause serious damage to macOS.

Writing an effective Apple Support Communities ... Apple Support Communities

apple melissa wrote:

My antivirus software

What is the name of the antivirus software?

You can only delete things on aTime Machine Drive from within Time Machine.

I find Windows 10 not very needy of Anti-virus SW.

I use PCs at work and notice our System Admins still use AV software. They support about 3500 Windows 10 machines.