Why it matters
Background images are discovered only after CSS is downloaded and applied, so they always start late and cannot use srcset or fetchpriority.
How to fix it
Render the hero visual as an <img> (with object-fit: cover) in the HTML, or preload it with <link rel="preload" as="image" fetchpriority="high">.
More performance rules
void perf reports 25 rules in this category. Core Web Vitals and bytes: LCP, CLS, TBT, TTFB, JavaScript, CSS, fonts, images, caching and compression, measured as the median of several runs on a throttled mobile and a desktop profile.
image-budgetImage transfer exceeds the budgettoo-many-requestsPage makes many requestslcp-image-lazyLCP image is lazy-loadedlcp-image-no-priorityLCP image has no fetchpriority="high"image-oversizedImage is much larger than its rendered sizeimage-legacy-formatImage served in a legacy formatimages-missing-dimensionsImages without width/height or aspect-ratiorender-blockingRender-blocking resources delay first paint