The mentioned file that missing is located upstream in https://github.com/miniupnp/miniupnp/tree/miniupnpd_2_3_1/miniupnpd/netfilter_nft/scripts
and the upstream configuration options that we think are missing to match vyos chains is https://github.com/miniupnp/miniupnp/blob/miniupnpd_2_3_1/miniupnpd/miniupnpd.conf#L77