https://join-lemmy.org/docs/users/02-media.html

Lemmy also allows sharing of images and videos. To upload an image, go to the Create post page and click the little image icon under the URL field. This allows you to select a local image. If you made a mistake, a popup message allows you to delete the image. The same image button also allows uploading of videos in .gif format. Instead of uploading a local file, you can also simply paste the URL of an image or video from another website.

Note that this functionality is not meant to share large images or videos, because that would require too many server resources. Instead, upload them on another platform like PeerTube or Pixelfed, and share the link on Lemmy.

Tldr: use the website not an app, there is direct upload, else, see peertube/pixelfed/catbox.moe/redgifs