/etc/systemd/system/network-mirrored.service

network-mirrored.service

[Unit]
Wants=network-pre.target
Before=network-pre.target shutdown.target

[Service]
User=root
ExecStart=/bin/sh -ec '\
  [ -x /usr/bin/wslinfo ] && [ "$(/usr/bin/wslinfo --networking-mode)" = "mirrored" ] || exit 0;\
  echo "\
  add chain   ip nat WSLPREROUTING { type nat hook prerouting priority dstnat - 1; policy accept; };\
  insert rule ip nat WSLPREROUTING iif loopback0  ip daddr 127.0.0.1 counter dnat to 127.0.0.1 comment mirrored;\
  "|nft -f -\
'
ExecStop=/bin/sh -ec '\
  [ -x /usr/bin/wslinfo ] && [ "$(/usr/bin/wslinfo --networking-mode)" = "mirrored" ] || exit 0;\
  for chain in "ip nat WSLPREROUTING";\
  do\
    handle=$(nft -a list chain $chain | sed -En "s/^.*comment \\"mirrored\\" # handle ([0-9]+)$/\\1/p");\
    for n in $handle; do echo "delete rule $chain handle $n"; done;\
  done|nft -f -\
'
RemainAfterExit=yes
[Install]
WantedBy=multi-user.target

you can try it.

$ sudo systemctl --now enable network-mirrored

Very grateful for this, spent countless hours trying to figure it out, no amount of gpt could save me.