Here:

server {
    listen 443 quic;
    listen [::]:443 quic;
    listen 443 ssl;
    listen [::]:443 ssl;
    server_name jellyfin.kitsuna.net;
    http2      on;
    http3      on;
    quic_gso   on;
    tcp_nodelay on;
    # You can increase the limit if your need to.
    error_log /var/log/nginx/jellyfin.access.log;
#    ssl on;
#    ssl_certificate /etc/nginx/certificate.crt;
#    ssl_certificate_key /etc/nginx/certificate.key;
#    ssl_protocols TLSv1 TLSv1.1 TLSv1.2; # don’t use SSLv3 ref: POODLE
        ssl_certificate /etc/letsencrypt/live/kitsuna.net/fullchain.pem;
        ssl_certificate_key /etc/letsencrypt/live/kitsuna.net/privkey.pem;
#        ssl_certificate_key /etc/letsencrypt/live/kitsuna.net/privkey.pem;
        ssl_protocols TLSv1.2 TLSv1.3;
        add_header Alt-Svc 'h3=":$server_port"; ma=86400';
        add_header x-quic 'h3';
        add_header Alt-Svc 'h3-29=":$server_port"';
    location / {
        proxy_pass http://10.159.4.12:8096/;
#       proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "upgrade";
        proxy_set_header Host $http_host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forward-Proto http;
        proxy_set_header X-Nginx-Proxy true;
    }
}