>> QUERY request can be cached

I have a weird feeling. Query body is encrypted by https. So CDN will not be able to cache results. In order to make it work right - whole topology of the internet should be redone. Caching on the backend server will not give any real gains for large scale apps.

The whole connection is encrypted by https, the request body is treated the same as the url, the headers or the response. The only unencrypted parts are the IP addresses/ports and the domain name (if SNI without ECH is used).

CDNs already terminate TLS connections so they can cache GET requests.