Hi,
beyond the obvious answer that someone will eventually say I am going respond with a few questions.
What are you seeing when you attempt to hit the proxy? error? have you looked at it with the F12 or developer tools in your browser/
Have you addressed the basic network requirements including either DNS entries that can resolve or at least etc. host file entries on the server to insure it can actually complete the redirection?
and have you simplified your setup and confirmed a simple redirector works?
I will assume you have a specific reason that you chose to use a server 2019 IIS instance as your reverse proxy. (I will avoid the entire lecture about basic auth and plain text password user names. windows accounts exsposure and all that blagh blagh because I am sure others will jump on that band wagon and preach)
But have you reviewed. the following documentation here for how it is done using Nginx ?
looking at your web config it seems your pattern is not quite right and you have defined preconditions and are not refencing them either.
Perhaps reviewing these links may also help.
Note there is rule inheritance to take into account as well as some other conditions that IIS require you to address as too. Things like . firewall ports certs and such as well as having all of the correct services and modules installed.
Good luck.
And Yes I have set up a IIS reverse proxy just because I could and it does work but I would not have it sitting in a public facing interface because nginx is so much easier to harden not exposing the windows services that IIS requires to make what your are doing work and less prone to be beat up on by the bad guys .