It is independent of that. The L4S standards change the IP layer to provide a more accurate ECN congestion signal , any transport protocol can then take advanta

It is independent of that. The L4S standards change the IP layer to provide a more accurate ECN congestion signal , any transport protocol can then take advantage of it. There are versions of TCP and QUIC that do so, in theory a version of uTP could be made to do so as well. However, from a brief look, uTP is designed for background transfers for which latency is not important, so there is no particular need to do so.