Downloading Pinterest media on iPhone works directly in Safari with no app installation. Copy a public Pin link in the Pinterest app using the Share menu, then open PinSaver4K in Safari and paste the link.
Choose an available format — MP4 video, MP3 audio, JPG image, PNG, or GIF — and tap download. The file goes to Safari's Downloads or to the Files app. From there you can move photos and videos to the Photos app when iOS supports that media type.
iOS sometimes restricts which file types can be saved directly to Photos. If a video does not appear in Photos, open it in the Files app first, then use the Share sheet to save it to Photos.
Only public Pinterest pins are supported. Private pins, secret boards, and content behind a login wall cannot be downloaded.