Images are served at one fixed size
What this means
This page has several images and not one of them declares a srcset. Every visitor therefore downloads the same file, so phones on mobile data pay for desktop-sized pixels they cannot display. Responsive image candidates are the single cheapest way to cut image bytes.
How to fix it
Add srcset with width descriptors plus a matching sizes attribute to content images, so the browser picks a candidate that fits the device. Most frameworks and image CDNs generate these automatically.
Fix effort
This check needs review: the change can be drafted for you, but a person has to approve the wording or choose the target before it ships.
Authoritative source
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