My nginx include for TLS A+ rating at ssllabs.com/ssltest using freenginx/1.31.1

TLS

# version 2026 may 23
ssl_certificate /etc/letsencrypt/live/my.domain.net/fullchain.pem;
ssl_certificate_key /etc/letsencrypt/live/my.domain.net/privkey.pem;
ssl_trusted_certificate /etc/letsencrypt/live/my.domain.net/chain.pem;

ssl_protocols TLSv1.2 TLSv1.3;
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;
ssl_prefer_server_ciphers off;

# Regenerate without -dsaparam: openssl dhparam -out /etc/ssl/dh4096.pem 4096
ssl_dhparam /etc/ssl/dh4096.pem;
ssl_ecdh_curve secp384r1;

ssl_session_cache shared:MozSSL:18m;
ssl_session_timeout 1d;
ssl_session_tickets off;

resolver 1.1.1.1 1.0.0.1 [2606:4700:4700::1111] [2606:4700:4700::1001] valid=2h;
resolver_timeout 9s;

# OCSP stapling is phased out by LE..
#ssl_stapling on;
#ssl_stapling_verify on;

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

# HTTP/3 — single consolidated Alt-Svc header
add_header Alt-Svc 'h3=":443"; ma=86400';

my include /etc/nginx/headers file contents;

add_header Strict-Transport-Security "max-age=31536000; includeSubDomains; preload" always;
add_header Referrer-Policy no-referrer-when-downgrade always;
# add_header Content-Security-Policy "default-src 'self' 'unsafe-inline' 'unsafe-eval'; img-src 'self' data:;" always;
add_header X-Frame-Options SAMEORIGIN always;
add_header X-Content-Type-Options nosniff always;
add_header X-XSS-Protection "1; mode=block" always;
add_header Feature-Policy "accelerometer 'none';ambient-light-sensor 'none';autoplay 'none';camera 'none';encrypted-media 'none';fullscreen 'self';geolocation 'self';gyroscope 'none';magnetometer 'none';microphone 'none';midi 'none';payment 'self';picture-in-picture 'none';speaker 'self';sync-xhr 'none';usb 'none';vibrate 'none';vr 'none';";

See https://hstspreload.org/ for the stuff relating to HSTS preload.

Note that as soon as some nginx config (could be any snippet you use for a server) has a 'new' add_header entry, all previously set ones are gone. So, here's my pro tip:
Put an
include /etc/nginx/headers;
after every new header you've set, or at the bottom of your server/vhost conf file.
Then test if the headers are still sent using ssllabs, https://www.immuniweb.com/ssl/ and/or https://securityheaders.com/

don't use
add_header Content-Security-Policy "default-src 'self' 'unsafe-inline' 'unsafe-eval'; img-src 'self' data:;" always;
it ruins all iframes and/or embedded remote media.