Why it matters
iOS home-screen bookmarks and some favicon consumers (including Google) use it.
How to fix it
Add app/apple-icon.png (180×180, opaque) or app/apple-icon.tsx.
References
More seo rules
void seo reports 60 rules in this category. What search engines need from the raw response: status codes, titles and descriptions in <head>, self-referencing canonicals, one h1, crawlable links, Open Graph, icons, robots.txt and a sitemap with real dates.
og-image-sizeog:image is smaller than 1200×630 or far from 1.91:1og-image-metaog:image:width/height missing or wrong, or og:image:alt missingtwitter-cardtwitter:card missingfaviconNo crawlable favicon in a Google-supported formatmanifestWeb app manifest missing or incompletetheme-colorNo theme-color metarobots-txt-unreachablerobots.txt returns 5xx/429 or times outrobots-txt-missingNo robots.txt