Any Bluesky post with an image or video attached will work. This also includes replies that have videos or images. If you want to download from a reply, you must enter the URL of the reply, not the post.

Example Image Post URL: https://bsky.app/profile/pixelartvillage.bsky.social/post/3lhk3hbmdrc2p

Example Video Post URL: https://bsky.app/profile/amazingnature.bsky.social/post/3lidgpobvlc27