I’m not sure this is contributing (or has even changed), but I was looking at the app-bridge.js CDN script and seeing how long that might load from various regions in the world.
The only thing that stood out to me was the Google Distributed Cloud header “X-Dc” which had a value of “gcp-us-central1,gcp-us-east1” regardless of where the request was initiated from.
That seemed unusual to me, but I’m not as familiar with GCP’s infrastructure. I don’t want to introduce any red herrings, but I know we faced a similar issue with our apps early on where the locality of our original CDN was not optimized and that made a big difference in our LCP scores once we corrected that.
EDIT: Looks like perhaps a similar issue was happening on storefronts: Investigating TTFB Variations on a Shopify Plus Store - #2 by Evaldas_Raisutis