It is supposed to replace TCP, but till then it sort of uses both. I use it only on Brave for Youtube/Google.

QUIC uses UDP for ports and connectionless transport, then adds the resiliency of TCP, the security of TLS 1.3, sprinkles in a dash of commands and version control from protocols like SMB, and then mixes in a set of new protocol concepts and efficiencies to create something entirely unique in the protocol world.