In PowerShell, run:
netsh interface portproxy add v4tov4 listenport=<host post> listenaddress=0.0.0.0 connectport=<wsl port> connectaddress=<wsl IP address>
e.g. forward port 8080 to port 8080
netsh interface portproxy add v4tov4 listenport=8080 listenaddress=0.0.0.0 connectport=8080 connectaddress=172.30.144.20
The actual IP address of the guest (not the gateway or whatsoever), can be obtained by commands like ip a.
netsh interface portproxy show all
netsh interface portproxy delete v4tov4 listenport=<host post> listenaddress=0.0.0.0
e.g. delete port 1234
netsh interface portproxy delete v4tov4 listenport=1234 listenaddress=0.0.0.0