Source Article: https://www.macworld.com/article/3447377/how-to-delete-photos-links-and-attachments-from-conversations-in-messages.html#tk.rss_all
Even as iPhones and iPads have dramatically increased internal storage, you can still fill them with music, photos, and videos—and attachments sent along with messages. Apple lets you delete these attachments, although it’s a bit of a convoluted process. Remarkably, these deletions don’t sync across your devices with Messages enabled in Cloud—even though the messages themselves do sync.
Here’s how to manage attachments in Messages.
Delete attachments in iOS and iPadOS
You can hold and tap to delete individual attachments from Messages in iOS.
