Bulk delete attachments messages

Many people have asked this, yet none of the answers have helped.

I need to bulk delete many photos from Messages conversations (AKA "attachments").

1. When I go to Messages > *the conversation > "i" icon in the top right > Photos > Show more, I CAN select multiple photos, but when I right-click> delete, only the one I right-clicked on is deleted. I've also tried keyboard delete shortcuts to no avail.
2. When I go to System Settings > General > Storage and try to go through the attachments there, it doesn't show all of them. I've been through them tediously and gotten to the end and noticed the majority of my media in Messages is missing.

Can we please have an answer? Many experts, including Apple Support personnel, have told users to do step 1 (above), but it does not work.

TYA!