I came across this post among others 2 years ago, while searching for the same thing.

This is now supported by AWS (UDP over IPv6 on NLBs) and was mentioned in this release - https://aws.amazon.com/about-aws/whats-new/2024/10/aws-udp-privatelink-dual-stack-network-load-balancers/

I was really excited as we've been waiting for this for 2 years but unfortunately, it requires SNAT and alters the client source IP - which might be ok for others, but is useless for us.

I hope that AWS can expand on this and have the ability to preserve the client IP, then it's an option. Shame this wasn't part of the solution since many other LBs have this functionality.