BrighData offer H3/QUIC but only in beta and you have to contact their sales team as far as I'm aware.

We (PingProxies) might be the only company to offer H3 to the proxy/QUIC to the target using the CONNECT-UDP method publicly. Although, it is in beta/unstable until I merge my changes into Rust's H3 library.

If you wanna play around with it, email me and I'll get you some credit. I think theres potential for stealth since outdated proxy clients/servers mean automated actors never use H3.

The proxy industry is full of another 100 companies saying they offer H3/QUIC, when they mean UDP proxying using SOCKS. I suppose the knowledge gap and what customers care about (protocol to end target) is very different to what I care about (being right/protocol to the proxy server).