Allowing an outgoing connection from Dom0

Try it like this:

cat << 'EOF' | sudo tee /etc/systemd/system/socat.socket
[Unit]
Description=socat

[Socket]
ListenStream=127.0.0.1:9090
Accept=true

[Install]
WantedBy=sockets.target
EOF
cat << 'EOF' | sudo tee /etc/systemd/system/socat@.service
[Unit]
Description=socat

[Service]
ExecStart=/usr/bin/socat STDIO EXEC:“‘qvm-run --pass-io SHServer socat STDIO TCP:localhost:80’”
StandardInput=socket
StandardOutput=inherit
EOF
sudo systemctl daemon-reload
sudo systemctl enable --now socat.socket