Due to Apple’s sandboxing, actual "downloader" apps are banned. However, "Save MMS to Gallery" is a Shortcut (Siri Shortcut) rather than an app. Install the shortcut, tap the MMS video in iMessage, hit "Share," and run the shortcut. It extracts the binary data and saves it as a watchable .mov file.
While primarily a backup tool, it is essential for those moving to a new phone or clearing space. Long-term archival of video attachments. mms video download top app
