udpReceiveBufferSize
The SO_RCVBUF size in bytes for the HTTP/3 UDP sockets, or 0 to use the system default.
Under load, an undersized receive buffer causes dropped datagrams, which QUIC treats as packet loss and recovers from at a significant throughput cost. Consider raising this (for example, to a few megabytes) for high-throughput deployments; the effective value may be capped by the operating system.