Can't get rid of the [fill in as appropriate] HTTP header is not set to

Hay varios avisos relativos a su configuración.

    La cabecera HTTP "X-Content-Type-Options" no está configurada como "nosniff". Esto es un riesgo potencial de seguridad o privacidad, y se recomienda ajustar esta configuración de forma adecuada.
    La cabecera HTTP "X-Robots-Tag" no está configurada como "noindex, nofollow". Esto es un riesgo potencial de seguridad o privacidad, y se recomienda ajustar esta configuración de forma adecuada.
    La cabecera HTTP "X-Frame-Options" no está configurada como "SAMEORIGIN". Esto es un riesgo potencial de seguridad o privacidad, y se recomienda ajustar esta configuración de forma adecuada.

Nextcloud version: 26.0.7
Operating system and version: Debian 11
Apache version: Apache 2.4.56
PHP version: 8.1

It was uploaded from 24.x version, but this issue was already present.

The output of your config.php:

{
    "passwordsalt": "***REMOVED SENSITIVE VALUE***",
    "secret": "***REMOVED SENSITIVE VALUE***",
    "trusted_domains": [
        "localhost",
        "nube.unau.edu.ar"
    ],
    "datadirectory": "***REMOVED SENSITIVE VALUE***",
    "0": "skeletondiretory\u2019 => \u2018\/var\/www\/nube\/core\/skeleton",
    "dbtype": "mysql",
    "version": "26.0.7.0",
    "trusted_proxies": "***REMOVED SENSITIVE VALUE***",
    "overwritehost": "nube.unau.edu.ar",
    "overwriteprotocol": "https",
    "overwritecondaddr": "^192\\.168\\.8\\.17$",
    "overwrite.cli.url": "https:\/\/nube.unau.edu.ar",
    "htaccess.RewriteBase": "\/",
    "dbname": "***REMOVED SENSITIVE VALUE***",
    "dbhost": "***REMOVED SENSITIVE VALUE***",
    "dbport": "",
    "dbtableprefix": "oc_",
    "dbuser": "***REMOVED SENSITIVE VALUE***",
    "dbpassword": "***REMOVED SENSITIVE VALUE***",
    "installed": true,
    "instanceid": "***REMOVED SENSITIVE VALUE***",
    "loglevel": 0,
    "maintenance": false,
    "theme": "",
    "force_language": "es",
    "force_locale": "es",
    "default_phone_region": "ar",
    "mysql.utf8mb4": true,
    "mail_smtpmode": "smtp",
    "mail_smtpsecure": "tls",
    "mail_sendmailmode": "smtp",
    "mail_from_address": "***REMOVED SENSITIVE VALUE***",
    "mail_domain": "***REMOVED SENSITIVE VALUE***",
    "mail_smtpauth": 1,
    "mail_smtphost": "***REMOVED SENSITIVE VALUE***",
    "mail_smtpport": "587",
    "mail_smtpname": "***REMOVED SENSITIVE VALUE***",
    "mail_smtppassword": "***REMOVED SENSITIVE VALUE***",
    "memcache.local": "\\OC\\Memcache\\APCu",
    "app_install_overwrite": [
        "epubreader"
    ],
    "preview_max_x": "512",
    "preview_max_y": "512",
    "jpeg_quality": "60",
    "memcache.distributed": "\\OC\\Memcache\\Redis",
    "memcache.locking": "\\OC\\Memcache\\Redis",
    "redis": {
        "host": "***REMOVED SENSITIVE VALUE***",
        "port": 6379
    }
}

As this instance is behind a reverse proxy, here’s corresponding setup

server {
    listen 443 ssl http2;

    server_name DOMAIN;

    include /etc/nginx/snippets/location-letsencrypt.conf;
    include /etc/nginx/snippets/ssl-params.conf;

    ssl_certificate /etc/letsencrypt/live/DOMAIN/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/DOMAIN/privkey.pem;

    client_max_body_size 0;
    underscores_in_headers on;

    location / {

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

       proxy_hide_header Upgrade;
       proxy_hide_header X-Powered-By;
       add_header Content-Security-Policy "upgrade-insecure-requests";
       add_header X-Frame-Options "SAMEORIGIN";
       add_header X-XSS-Protection "1; mode=block" always;
       add_header X-Download-Options "noopen" always;
       add_header X-Content-Type-Options "nosniff" always;
       add_header Cache-Control "no-transform" always;
       add_header Referrer-Policy no-referrer always;
       add_header X-Robots-Tag "noindex, nofollow";

       proxy_set_header Host $host;
       proxy_set_header X-Real-IP $remote_addr;
       proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
       proxy_set_header X-Forwarded-Proto $scheme;
       add_header Front-End-Https on;

       proxy_headers_hash_max_size 512;
       proxy_headers_hash_bucket_size 64;

       proxy_buffering off;
       proxy_redirect off;
       proxy_max_temp_file_size 0;

       #Timeout para archivos grandes
       proxy_connect_timeout 1000;
       proxy_send_timeout 1000;
       proxy_read_timeout 1000;
       send_timeout 1000;

       proxy_pass http://INTERNAL-IP/;

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

    }

    location /.well-known/carddav {
      return 301 $scheme://$host/remote.php/dav;
    }

    location /.well-known/caldav {
      return 301 $scheme://$host/remote.php/dav;
    }

    access_log /var/log/nginx/DOMAIN/access.log;
    error_log /var/log/nginx/DOMAIN/error.log;

}