https installation problem

[iEiEi]

On top of your /etc/nginx/conf.d/jellyfin.conf you define a redirect from http (Port 80) to https (Port 443). That's ok and should be done.

server {
    listen 80;
    listen [::]:80;
    server_name jellyfin.domain.tld;

    # Uncomment to redirect HTTP to HTTPS
    return 301 https://$host$request_uri;
    }

In your setup for https, however, you specify that a call of the document root should be redirected to http - this leads to an endless loop:

location = / {
    return 302 http://$host/web/;
    #return 302 https://$host/web/;
    }

And that's working in my configuration for secure connections:

location = / {
    return 302 https://$host/web/;
    }

Regards
Achim