Oversized image
What it means
These images are larger than 100 KB. Images are usually the heaviest part of a page, and an oversized one delays everything that follows it.
How to fix it
Serve WebP or AVIF instead of JPEG or PNG, resize to the dimensions actually displayed rather than relying on the browser to scale down, and use srcset so small screens get small files. Add loading="lazy" to images below the fold, but never to the main image at the top of the page, which should load as early as possible.
Finding it in CrawlStat
After a crawl, open Issues and pick Oversized image. Click Show all in Pages to filter the Pages table to the affected pages, or Export affected to hand the list to whoever owns the fix. Audit ID: image_oversized.