Hello, I am following Setting up and NGINX proxy Set up an NGINX proxy - Mattermost documentation and found some mistakes in your docs.
listen 443 ssl http2;
This is deprecated. Must be:
listen 443 ssl;
http2 on;
sudo touch /etc/nginx/sites-available/mattermost on Ubuntu
No longer valid. At least in Ubuntu 24.04. There is no directory sites-available. It is conf.d