WebTransportDatagramDuplexStream: свойство maxDatagramSize

const url = "https://example.com:4999/wt";

async function initTransport(url) {
  // Initialize transport connection
  const transport = new WebTransport(url);

  // The connection can be used once ready fulfills
  await transport.ready;

  const datagrams = transport.datagrams;

  // get maxDatagramSize
  console.log(datagrams.maxDatagramSize);
}