Apple Mail - 'remove attachments' is greyed out
I'm using Apple Mail (16.0) on a MacBook Air (M1) running Ventura 13.6. The option to 'remove attachments' under Message in Mail is permanently greyed out and trying to delete attachments results in the email being deleted.
I sometimes get emails with quite large graphic attachments and purely to save space I would like to delete the attachment but retain the email. Can anyone tell me what I am doing wrong?
Thanks in advance.
MacBook Air 13″, macOS 13.6