ok
donc change le début par
server {
listen 80 default_server;
listen 443 default_server ssl http2;
server_name _;
index index.html index.php;
charset utf-8;
client_max_body_size 10M;
ssl_certificate /etc/letsencrypt/live/bkc.fr/fullchain.pem;
ssl_certificate_key /etc/letsencrypt/live/bkc.fr/privkey.pem;
include /etc/nginx/conf.d/ciphers.conf;
access_log /var/log/nginx/rutorrent-access.log combined;
error_log /var/log/nginx/rutorrent-error.log error;
error_page 500 502 503 504 /50x.html;
location = /50x.html { root /usr/share/nginx/html; }
auth_basic "seedbox";
auth_basic_user_file "/etc/nginx/passwd/rutorrent_passwd";