It's your app and the sites the gifs are hosted on, not Lemmy. Most instances aren't going to host gifs because they take up a decent chunk of space.
For example: link (its a pussy, don't click the link if you don't like that sort of thing I guess).
But that is hosted on lemmy (at least I assume based on the url for the image) and I am viewing it on a web browser, no app. If you expand that gif, it doesn't play. But if you click the link it plays. That's what I mean.
That's one of the use cases that's not optimized yet, but there are others. Just some of the ones for desktop alone and there are more for each client:
Seeing as some clients have working examples of making this work, I personally believe it needs to be fixed in lemmy-ui. So I took a look and there are some open feature requests for video embedding but they don't really cover your use case or the ones I listed but they are similar:
https://github.com/LemmyNet/lemmy-ui/issues/1852
https://github.com/LemmyNet/lemmy-ui/issues/1215
https://github.com/LemmyNet/lemmy-ui/issues/709
I suspect that we (lemmynsfw users) are the ones that are most impacted by this issue and that it is unlikely to make it to the maintainers for a while. If we really wanted to fix it, someone could gather all the issues and make sure that we submit them all to lemmy ui.
A quicker yet more difficult way may be to find out if any of the more open source clients figured out this issue and ask them what they did to fix it. Then try to find someone that could convert that code to whatever lemmy-ui is written in and submit it ourselves to the project. Or just send it to our admins to test it out.
Here is a discussion from the folks from Sync that adds more context about the challenge. I think it is something the clients have to figure out one at a time
Connect did some changes in their last update for that. At least redgifs autoplays since then.
