I have been doing it this way but it doesn't look like this include all the attachments. I don't know what the selection is based on. Also a few have reappeared perhaps this is getting pulled from iCloud.
There are some contacts that I have been sent a lot of photos for work that I would like to bulk delete these.... but not delete the whole conversation.
The iCloud question is if I delete the attachments the way you say or through messages on MacOS does this also delete from iCloud backup or will they just be pulled again when scrolling through messages. Is there a way to delete the attachments so that it deletes on iCloud too.