My understanding is that the way it works is that your proxy server pretends to be a server ran by some legitimate entity (e.g. cloudflare, aws, etc.). When setting up the server, you will instruct it respond using the cert from the façade domain. To the censor, it would appear that you are approaching a server ran by the legitimate entity. If the censor becomes suspicious of the IP and decides to probe the server to see if it is a circumventing proxy, it would see valid certs but no actual content (as if the server at the IP is broken/down). However, there is actually a secret path+password that you can use to make the server aware that you are a real client and the proxy server would start proxy your traffic normally.