It seems like i found the problem. One just always should mention a port number upon construction of Deno.QuicEndpoint despite it being an optional option. So upon construction with the port number 443 like this new Deno.QuicEndpoint({port:443}), any HTTPS requests through WebTransport will reach their destination automatically just like regular HTTPS requests and it seems that HTTPS server and QUIC one do not even block each other when they are hosted on the same port number.