I sent an email via Apple Mail and (Virus Error) was added to the beginning of the subject line. Needless to say, this worried the recipients but multiple tests, with Apple Support helping, have indicated no virus present anywhere.
Subsequent emails with the same recipients and attachments did not have the same problem. Apple Support focused on my MacBook as the problem. I think it happened as the email was routed around.
MacBook Pro 16″, macOS 14.3