LinkedIn Article Cover size: 1920 x 1080 pixels.

LinkedIn's help page for publishing articles states that the optimal cover image is 1920 by 1080 pixels and that covers are cropped to 16:9, and it lists JPEG, JPG, PNG and WEBP as the accepted file types for the cover. It gives no file size limit for images, only a 5 GB cap for video, so there is no maxMB below rather than a guessed one.

The cover runs across the top of the article at full width, which on a computer is considerably wider than the feed column, so this is one of the few places where a large export earns its pixels. When the article is shared into the feed it appears as a card closer to 1.91:1, and that crop takes a slice off the top and bottom of the 16:9 image. Keep a title or a subject away from those edges.

A photograph or a flat graphic both work; a screenshot of dense text does not, because the card version shrinks to a few hundred pixels wide in the feed. If you want a matching square or portrait teaser for other networks, build it from the same artwork rather than cropping the 16:9 file, since a 1080 by 1350 crop out of a wide cover keeps only the middle third.