Connection refused & Looking for advice on running two sites

Hello everyone,
I just switched my webserver from Apache to nginx and I have some problems. I did follow this tutorial: https://github.com/groovemonkey/hands_on_linux-self_hosted_wordpress_for_linux_beginners

I did open this post on StackExchange but since I couldnt get any good answer, I thought I could try it here.
https://unix.stackexchange.com/questions/475064/nginx-cant-bind-to-port-already-in-use-although-no-tasks-running-on-that-por/475136#475136

Firstly, I had the issue that nginx couln‘t bind the port. I could fix it after many hours of frustration by simply replacing my site.conf with the default.conf file in the sites-enabled folder. My system is Linux Mint.

It would be great if we could get it to work, all configs are in the stackexchange post. I‘m afraid I can‘t post them here because I‘m on a mobile device. I think it‘s worth mentioning that I still want to use the old wordpress site.

After it is up and running I have a question: what would be the easiest way to make a subdomain that points to a discourse forum?
Thank you very much in advance :)