Core Web Vitals are field measurements from real users. If those users are not next to your origin, LCP is a geography score until you put HTML and the LCP image on an edge.
LCP is a delivery problem first
Largest Contentful Paint is often a hero image or heading in the first HTML. Caching that HTML and transforming the image to a sane size at Cloud CDN (WebP or AVIF, resized) removes origin RTT from the critical path.
Self-host fonts on the same CDN hostname to avoid a third-party font round trip. See CDN for web fonts.
INP is mostly your JavaScript
Interaction to Next Paint cares about main-thread work. A CDN will not make a 400 kB framework cheaper. It will make the script arrive faster over HTTP/3 from a nearby PoP so parse can start earlier.
Do not expect Cloud CDN to replace code splitting. Do expect hashed bundles to be long-cached worldwide.
CLS and images without dimensions
If you resize at the edge, still reserve space in the layout. A fast image that pops in late still fails CLS.
Use width and height (or aspect-ratio) that match the transformed geometry you request.
Measure from the markets you sell to
Lab tests from the origin region will flatter you. Field data from another continent will not. 210+ PoPs exist so those field users hit cache.
Pair the CDN with Anycast DNS so the lookup is not the hidden vital.