TsgcQUICServer › Properties › Port
UDP port the server binds to and listens on for incoming QUIC connections.
property Port: Integer read FPort write FPort;80
QUIC runs over UDP, so Port is the UDP port the listener binds to. The property is inherited from the UDP server base class, whose constructor sets it to 80. That default is inherited plumbing rather than a sensible QUIC port, so always assign a port explicitly before calling Start. 4433 and 443 are the common choices for QUIC and HTTP/3.
The value must be set while the server is stopped, because the socket is bound when the listener is created. Make sure the chosen UDP port is open in any firewall, as UDP and TCP ports are filtered independently. Note that Port is public but not published by TsgcQUICServer, so it is assigned from code rather than in the Object Inspector.
oServer := TsgcQUICServer.Create(nil);
oServer.Port := 4433;
oServer.QUICOptions.SSLOptions.CertFile := 'cert.pem';
oServer.QUICOptions.SSLOptions.KeyFile := 'key.pem';
oServer.Start;