Can I move SSL certificate files from one server to another for the same domain?
Your listen 443 need to have ssl parameter to tell Nginx that all connections accepted on this port should work in SSL mode.
See example at https://nginx.org/en/docs/http/configuring_https_servers.html#single_http_https_server
Shown here for convenience:
server {
    listen              80;
    listen              443 ssl;
    server_name         www.example.com;
    ssl_certificate     www.example.com.crt;
    ssl_certificate_key www.example.com.key;
    ...
}