Nginx ingress, arguably the most popular reverse proxy for Kubernetes, is also lacking any HTTP3 support because of this slow progress. The related issue is 5y/o and the feature is now planned for its successor.
https://github.com/kubernetes/ingress-nginx/issues/4760
Wow, I didn't realize that about nginx. I've been using HAProxy with http3 for several months, and it's supported http3 for over 2 years.[0]