If you inspect traffic on YouTube or Facebook today, you won't see TCP. You will see UDP port 443. This is HTTP/3.
1. Head - of - Line Blocking(TCP's Flaw)
In HTTP / 2(TCP), if one packet gets lost, everything stops waiting for retransmission.
2. QUIC (UDP) Solves This
QUIC treats every stream independently. If Packet A is lost, Packet B is still delivered to the browser.
Check if your browser supports QUIC using our Connection Protocol check in the API.