The canonical UDT implementation does not come with encryption, however there are some older open source GitHub repos that have attempted to add TLS to UDT. The original author of UDT, Yunhong Gu, has a project called Sector/Sphere that adds some application-level encryption to file transfer if you want to check it out: http://sector.sourceforge.net/. We've added encryption for our algorithm though!

With respect to QUIC, I believe it was designed specifically to reduce the latency of HTTP connections by using multiple UDP flows and building the reliability/ordering guarantees at the application layer.

The problem with getting performance increases out of multiple, distinct traffic flows is that you become more and more unfair to other packet traffic as you increase the number of flows you are using. For example, if you use 9 TCP (or any other AIMD) flows to send a file over some link, and a tenth connection is started, you now are taking up to 90% of the available bandwidth (because AIMD flows are designed to be fair amongst themselves).