What LinkedIn tends to read
For a normal web page, LinkedIn uses the same core Open Graph fields as other networks: og:title, og:description, and og:image. og:site_name is useful when you want the site name to be explicit. Twitter card tags are not a substitute. If only twitter:image is set, LinkedIn will not treat that as the link image.
Image and text
A 1200×627 or 1200×630 image is a solid default. Use an absolute HTTPS URL that returns the image without a login. Titles that are specific beat titles that repeat the site name. The description should stand on its own when the reader never visits the page.
LinkedIn caches previews too. After you change tags, the post composer can keep showing the previous card until LinkedIn fetches the URL again. The estimate on this page is generated only from the HTML we just retrieved. It is not LinkedIn’s own renderer.
Check the image file itself with the OG image checker, or review every tag in the Open Graph preview.