> I have come across systems that use GET but with a payload like POST.

I think that violates the HTTP spec. RFC 9110 is very clear that content sent in a GET request cannot be used.

Even if both clients and servers are somehow implemented to ignore HTTP specs and still send and receive content in GET requests, the RFC specs are very clear that participants in HTTP connections, such as proxies, are not aware of this abuse and can and often do strip request bodies. These are not hypotheticals.