/etc/systemd/system/syncthing-discosrv.service.d/override.conf

 [Service] 
 ExecStart= 
 ExecStart=/usr/bin/syncthing-discosrv -db-dsn='file:///var/discosrv/discosrv.db -http

certbot certonly --email postmaster@adke.org --webroot -w /var/lib/letsencrypt -d adke.org -d www.adke.org -d siabn.adke.org -d mail.adke.org -d pad.adke.org -d disco.adke.org

nginx.conf

server { 
listen [::]:443 ssl http2; 
listen 443 ssl http2; 
# HTTP 1.1 support 
server_name disco.adke.org; 
include /etc/nginx/ssl.conf; 
include /etc/nginx/letsencrypt.conf; 
location / { 
    proxy_http_version 1.1; 
    proxy_buffering off; 
    proxy_set_header Host $http_host; 
    proxy_set_header Upgrade $http_upgrade; 
    proxy_set_header X-Real-IP $remote_addr; 
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for; 
    proxy_set_header X-SSL-Cert $ssl_client_cert; 
    proxy_pass http://127.0.0.1:8443; 
} 
}

As Discovery Server in syncthing setting set:
https://disco.adke.org/v2/