Auto-Set the Featured Image on Every Post

Yes. It applies to any post missing a featured image, so imported and legacy content get thumbnails without editing each post by hand.

No. It works at runtime only - no database writes and no duplicated media. Toggle it off and the original behavior returns instantly.

Then there's nothing to use, so the post has no featured image, exactly as before. Posts that already have a featured image are never overridden.

Yes. The chosen image is also emitted as the og:image, so shared links get a preview even when no featured image was set.

The first one in the content, reading top to bottom - the same image a reader sees first. That is almost always the one you would have chosen manually as the thumbnail.

Always. A featured image you set by hand takes priority and is never replaced. The automatic pick only fills the gap when the field is genuinely empty.

Yes. It hooks the featured-image lookup itself rather than a specific screen, so any post type that supports featured images benefits - custom post types and products included.

No. The lookup only runs for posts that are actually missing a featured image, and it writes nothing to the database, so there is no extra load on posts that already have one.