It’s usually a video on RedGifs. They intentionally make it difficult to view their videos anywhere but directly on their website. You can view them by opening the link in your browser with the chain icon in the middle.

Could you look up where the media is hosted, directly on LemmyNSFW or somewhere else. Voyager doesn’t seem to show this so you would have to open the post in a browser. Below is a browser screenshot where I posted the same image twice, once by uploading it directly to my instance (https://infosec.pub) and once by linking to the image on an external host (https://commons.wikimedia.org). For reference, the posts can be found at [email protected].