Pinterest does not treat every animation the same way. Depending on how a pin was created and when, the platform may keep a genuine animated GIF file, or it may store a silent MP4 and simply loop it so the pin reads as animated to anyone scrolling. Nothing in the interface distinguishes the two, and both look identical in a board.
That inconsistency is the root of the most common complaint about saving from Pinterest: you right-click an obviously animated pin, save it, open the file, and get one frozen frame. What happened is that the browser wrote out the poster image the page was displaying rather than the underlying media. The animation was never in the file you saved.
Fetching the stored media directly sidesteps that, but it means you sometimes receive an MP4 where you expected a GIF. That is not a failure — it is what Pinterest actually holds for that pin, and no tool can produce a GIF the platform never stored.
If you specifically need an animated GIF, it has to be rebuilt from the video, and the trade-offs are worth knowing before you choose it. GIF supports only 256 colours per frame, so gradients band visibly, and the resulting file is usually several times larger than the MP4 it came from. For most modern uses — chat apps, Slack, Discord, most forums — a short silent MP4 loops exactly like a GIF and is the better file. Rebuild a real GIF only when something refuses video outright.