It would only be possible if the server asks the client how he 'looks' like, but even then, he can lie about it as well as a person can lie on the phone about how he looks. To detect what the client actually 'looks' like is as impossible to the server as it is to you to detect how another person looks through the phone. But if the client sends a lot of 'move me to X' messages, just barely in the range of the server not recognizing them as invalid, you can speed hack, fly and such - which is basically what hacked clients do and what Anti Cheats exists for - to detect these 'illegal' messages.
If Client C would now suddenly send 'teleport me to X', the server would obviously deny that message. If Client A sends 'break this block' or Client B sends 'break this block', doesn't really matter to the server, he is only interested in the message if it has the right format and will only answer if the message is also valid. The clients all send the 'same messages' to the server and the server only accepts certain messages. Check out Future for a client that supports newer versions of Minecraft. More bypasses for more servers coming soon. Undetectable and High Quality Flux is undetectable on Hypixel (Watchdog), NCP, AACv3 and AACv4, providing high quality bypasses since 2016.
features that seperate flux from the competition. You can imagine something similiar with clients and server. Impact supports Minecraft 1.16.5, 1.15.2, 1.14.4, 1.13.2, 1.12.2, 1.12.1, 1.12, and 1.11.2. Flux Client A clean and visually appealing client made to bypass hypixel. Question: can you tell how someone looks just by talking to them on the phone?
