I am working on my own KMP app that uses HTTP/3 / QUIC under the hood, and so I made a project
Kiche project that provides KMP bindings (Android / iOS / JVM) to Cloudflare Quiche, plus Ktor implementations of client engine, server engine, webtransport module, and an adaptive engine that lets you use Kiche alongside with an HTTP/2 engine of your choice, feel free to check out (as usual, no warranty provided and there might be some rough edges).