If you use a direct file link, which for gifs on imgur would be .mp4 instead of gifv (which isn't actually a direct file link), the video will embed in some clients. I've not seen it work in a comment, but posts will have an embedded player if the url submitted is to a direct video file.
Alternatively, if you're posting a gif or don't need sound, turn it into a .webp. The file will be much smaller than an actual .gif, and play in most clients. It also works in a comment, like so:
Not too sure, the one in this comment did not load for me. I should note that im on Boost for lemmy and just take them directly from my galarie, so Boost uploads these that way, not sure if there is another way though. Before it worked just fine, but on that day all the things I uploaded kinda janked
Boost probably inherited the habit of reddit apps to use imgur as an image host, then. Most apps upload to the pict-rs server provided by the lemmy instance, not imgur.
Does boost have support for animated webps? Edit: tested it, it does load, but does mot animate.
The gifv is an imgur thing (they convert gifs to mp4 files), but you can edit the post and just change the .gifv to .mp4, that will at least make the video work in some clients.
Stills should work just fine, as long as boost is using the direct file link after upload.
Video support on lemmy is a little tricky atm, depends on the client, but gifs and webp both work, as long they are direct links to actual such files. Which you can't do with gifs on imgur, as they turn them into video files.