Cleaning up iMessage attachments on iPhone AND iCloud

I have an iPhone 16 Pro Max on iOS 18.0 and iCloud+. I would like to keep all of the text history in all of my iMessage conversations but delete the photo and video attachments in all locations since those are what take up the majority of the space.

Things I've done so far:

iPhone

• Messages > select a conversation > tap name at the top > tap See All under Photos > (painstakingly slow since drag to select is not enabled) select all photos and delete
• Messages > select the same conversation > scroll up and observe there are still photos displayed in the conversation Why?
• Photos > Recently Deleted > 0 photos available to permanently delete Is there somewhere else I need to go to permanently delete these photos from this conversation?
• Settings > General > iPhone Storage > Messages > Photos indicates 6.28 GB > tap on Photos > 0 photos ... So what is using 6.28 GB? ... same thing happens with Videos except they're taking up 9.12 GB, Why? Also, the Documents & Data total indicates 11.76 GB which is less than the total of Photos and Videos (~15.40 GB). I've already tried to restart my iPhone. The problem persists.

iCloud

• Settings > My Profile > iCloud > Saved to iCloud Messages (25.3 GB) > observe 'Use on this iPhone' is enabled and 'Keep Messages' is set to 'Forever.' This is because I want to be able to receive and send messages from any of my Apple devices. I know I can change 'Keep Messages' to 1 year but then I would lose all of the text history older than 1 year. I'm ok with losing the attachments older than that, but not the texts. How do I do this?