Yes to the routing, no to the port thing. A URL (i.e. qbittorrent.yourdomain.tld) is simply much easier to remember and work with than an IP:Port combination (i.e. 87.253.143.32:8080).
It also has a security benefit, because if you expose your server to the internet, you only have to open the http(s) ports of your webserver in your firewall and not the ports of the applications behind it. The webserver will do all the communication with your backend and then serve the information to the requester, so you have a buffer in-between.
Less open ports = less potential points of attack.
At least that’s how I understand it. I’m just a hobbyist, so if I got it wrong, feel free to correct me.
Frankly, if you want to use nginx as your reverse proxy and don’t want to get too deep into nginx configuration files and stuff, check out Nginx Proxy Manager. It’s a GUI frontend that automatically gets you SSL certificates for your subdomains, super useful.
Let me be the Devil’s advocate here.
You/we (as users) are being compensated by being permitted onto whatever service is being gatekept by Recaptcha. We profit further by having that service not be completely tainted by bots. Sure, recaptcha ain’t even close to perfect and can be easily bypassed, but any barrier of entry is better than none at all.
Google profits by getting free training for their models.
And the service provider profits by saving on bandwidth, moderation etc., which in turn benefits the users too in the form of a less degraded service.
There are many things to dislike about Google and what they are doing to the web. Recaptcha should not even be in your top 100.