I don't think you can do anything; Imgur itself fucked this up a while ago so that even if you, yourself, have a direct link and it seems to work, everyone else gets sent to the page with the ads, and not the direct image.
I just reupload them somewhere else. I should check out PixelFed, actually.
When it fetches the metadata for the post Link, that's the embed_video_url that was returned from Imgur. Lemmy UI may not show the embed video but the thumbnail instead. You can always use image markup in the post body to embed it, though.
On Firefox it was as easy as right clicking on the image and copying the link.
Chrome refused to show the link though, and I would guess others e.g. Safari would be more similar to Chrome.
Solution: Firefox greatly simplifies such things:-D.
Edit: also, I don't know about whatever UI method you used - an app or the webpage one or whatever. What I did here was to just type out exclamation markm(this is what caused an image to be auto-loaded in the Fediverse), straight braces some alt text, parentheses with the image link inside, then check the Preview to make sure it would load before posting. Like so:
My issue is that nothing wants to play unless it’s in the body of my post, whereas I intend to offer it embedded beside the title. I found another source and created a third, but all of them are just links and nothing is fetched by Lemmy. Uploading to Lemmy also doesn’t work as Lemmy doesn’t host .mp4 videos, so I decided to convert it to a .gif to post later. I do declare, this has been a most frustrating issue.
Ah, you wanted the movie to play from the title or post text rather than comment? Yeah, I suspect that is not allowed. I for one find it highly distracting when scrolling downwards and things are moving around on their own, plus there's sound to consider, so I am kinda glad for that rule tbh - you might mean well here but anything that can be abused will be by someone with lower ethical standards:-(. I offer that as a potential reasoning as to why you might be struggling with making this happen.
But also, the Fediverse is not very technically advanced yet, compared to e.g. Reddit, but I think you are approaching it the right & only way: direct experimentation, leaning towards gifs, etc. Things might also vary by instance and if we are talking titles I believe by community, bc of how I've seen news articles set up differently. i.e. that text goes through a different filtering process, which presumably does not load images especially those with sound embedded. But I don't really post here only comment so that's all I got. One day such things will become easier but for now, the developers are working on other more pressing issues, like how to remain afloat against the constant DDoS attacks:-(. But I do wish you a happy resolution to this, to find something that you can live with:-).