Remove Attachments in Apple Mail is not working in Catalina

I updated to Catalina OS 10.15.7, and I noticed that when I'm in Apple Mail, the "Remove Attachments" option (under the "Message" menu) appears to do absolutely nothing.

I have a ton of emails that I would like to keep, but I don't need all these massive attachments. Rebuilding the mailbox does not seem to help.