load balancing – How to improve TTFB on NGINX?

I have a long TTFB (1.6 sec) and find the reason for this.
My stack is server (nginx + php-fpm) and load balancer on Hetzner and Cloudflare.
Are there too many redirects and therefore the waiting time is long?

My load balancer of Hetzner:

nginx.conf

server {
    listen 80;
    server_name www.example.com api.example.com;
    return 301 https://www.example.com$request_uri;
}

server {
  listen 443 ssl http2;
  server_name  www.example.com api.example.com;
  root /var/www/app/public_html/web;

  ssl_certificate /etc/letsencrypt/live/example.com-0001/fullchain.pem;
  ssl_certificate_key /etc/letsencrypt/live/example.com-0001/privkey.pem;
  ssl_dhparam /etc/nginx/ssl/dh2048.pem;

  ssl_session_timeout 5m;

  ssl_session_cache shared:TLS:2m;
  ssl_buffer_size 4k;
  add_header Strict-Transport-Security "max-age=31536000;" always;


  include "conf.d/server_ssl.conf";
  include conf.d/drupal-prelive.conf;
  include conf.d/php_fpm_status-prelive.conf;

  access_log /var/log/nginx/nginx-app1.log main;
  error_log /var/log/nginx/nginx-app1-error.log;

  proxy_buffer_size   1024k;
  proxy_buffers    4 1024k;
  proxy_busy_buffers_size   1024k;

  proxy_read_timeout 300;
  proxy_connect_timeout 300;
  proxy_send_timeout 300;

}

Page rule of Cloudflare: