Selfhosted

Maybe have a look at https://nginxproxymanager.com/ as well. I don't know how difficult it is to install since I never used it, but I heard it has a relatively straight-forward graphical interface.

Configuring good old plain nginx isn't super complicated. It depends a bit on your specific setup, though. Generally, you'd put config files into /etc/nginx/sites-available/servicexyz (or put it in the default)

server {  
    listen 80;  
    server_name jellyfin.yourdomain.com;  
    return 301 https://$server_name$request_uri;  
}  

server {  
    listen 443 ssl;  
    server_name jellyfin.yourdomain.com;  

    ssl_certificate /etc/ssl/certs/your_ssl_certificate.crt;  
    ssl_certificate_key /etc/ssl/private/your_private_key.key;  
    ssl_protocols TLSv1.2 TLSv1.3;  
    ssl_ciphers 'ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384';  
    ssl_prefer_server_ciphers on;  
    ssl_session_cache shared:SSL:10m;  

    location / {  
        proxy_pass http://127.0.0.1:8096/;  
        proxy_http_version 1.1;  
        proxy_set_header Upgrade $http_upgrade;  
        proxy_set_header Connection 'upgrade';  
        proxy_set_header Host $host;  
        proxy_cache_bypass $http_upgrade;  
    }  

    access_log /var/log/nginx/jellyfin.yourdomain_access.log;  
    error_log /var/log/nginx/jellyfin.yourdomain_error.log;  
}  

It's a bit tricky to search for tutorials these days... I got that from: https://linuxconfig.org/setting-up-nginx-reverse-proxy-server-on-debian-linux

Jellyfin would then take all requests addressed at jellyfin.yourdomain.com and forward that to your Jellyfin which hopefully runs on port 8096. You'd use a similar file like this for each service, just adapt them to the internal port and domain.

You can also have all of this on a single domain (and not sub-domains). That'd be the difference between "jellyfin.yourdomain.com" and "yourdomain.com/jellyfin". That's accomplished with one file with a single "server" block in it, but make it several "location" blocks within, like location /jellyfin

Alright, now that I wrote it down, it certainly requires some knowledge. If that's too much and all the other people here recommend Caddy, maybe have a look at that as well. It seems to be packaged in Debian, too.

Edit: Oh yes, and you probably want to set up Letsencrypt so you connect securely to your services. The reverse proxy would be responsible for encryption.

Edit2: And many projects have descriptions in their documentation. Jellyfin has documentation on some major reverse proxies: https://jellyfin.org/docs/general/post-install/networking/advanced/nginx

That question is a little bit out of the scope of a forum like this. A question like that would better be answered by the nginx documentation. Sometimes the project documentation might have a blurb about nginx configuration specific for that project. For example, Immich.

For the most part, you only have to reference the nginx documentation. I've never looked at the Immich config above until now, and my Immich server works great.

I've had a reverse proxy for years, but the config files are very foreign to me because I use Nginx-Proxy-Manager. NPM makes nginx usable for dummies like me, at the expense of gaining a deeper understanding of how it works. I'm ok with that, but you might feel differently.