@Keralewd@lemmynsfw.com provided this guide in the comments of the original post:
I’ve only had success with posting links to animated WebP files, which preview and display correctly in the default web UI. It doesn’t seem to work perfectly across the variety of apps and their handling of images though.
I think @NotAGuyInAHat mentioned that they use EZgif to do it. I generate them locally with FFmpeg, though that’s a little technical.
I was just passing through and thought I would throw in my two cents on this, as someone with a bit of experience. Session and SimpleX both work as ‘secure and private group chat’ platforms, as they are E2EE and require no phone numbers/other private information. SimpleX is a little more feature rich, but I’ve found Session more stable (although SimpleX is improving. They also lack the geek-curve @ExhibiCat@lemmynsfw.com mentioned, as you don’t have to do much more than pick a username to start chatting (unless you want to dig into all the technical settings). Depending on what you are looking for in a chat app, you may want to check them out.
e: fixed the link for SimpleX