Why does the "Key Exchange" and "Cipher Strength" test at ssllabs.com pass 90?

Question

Nginx

I got a Let's Encrypt certificate, I want to achieve 100 points in all parameters, but I can't get through "Key Exchange" and "Cipher Strength", tell me why?

options-ssl-nginx.conf

ssl_session_cache shared:le_nginx_SSL:10m;
ssl_session_timeout 1440m;
ssl_session_tickets off;

ssl_protocols TLSv1.3 TLSv1.2;
ssl_prefer_server_ciphers off;

ssl_ciphers "ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384";

add_header Strict-Transport-Security "max-age=31536000; includeSubDomains" always;

Answer 1

1.
For Cipher Strength 100, you need to get rid of "SHA256" in nginx:
instead of the ssl_ciphers line, you need three of these (fresh nginx, of course):

ssl_conf_command Ciphersuites TLS_AES_256_GCM_SHA384;
ssl_conf_command CipherString ECDHE-RSA-AES256-GCM-SHA384;
ssl_ciphers 'TLS_AES_256_GCM_SHA384:ECDHE-RSA-AES256-GCM-SHA384';

2.
For Key Exchange 100, you need to INITIALLY issue a certificate in rsa 4096 bits
PS
Only what is it for? The connection will be established more slowly, you will lose some clients with old systems / browsers - they simply will not be able to log in!