$ iptables: DROP 100% of UDP to/from port 4433 (TCP untouched); server is the h3 server
$ java src/Fallback.java https://localhost:4433/hello 120
request HTTP_3 (ANY)       -> HTTP_2                                                                 after  3397 ms
client HTTP_3 (ANY)        -> HTTP_2                                                                 after    46 ms
request HTTP_3_URI_ONLY    -> java.net.ConnectException: No response from peer for 30 seconds        after 60014 ms