First, copy this file into your web root directory and access it from your browser. Then, just replace your server block with the following right before you create an admin user and set up the database (replace [X.X.X.X], [mydomain], and [port] with your own info):

    server_name nextcloud.[mydomain].com www.nextcloud.[mydomain].com;
    listen X.X.X.X;

    listen X.X.X.X:443 ssl http2;
    ssl_certificate /home/[mydomain]/domains/nextcloud.[mydomain].com/ssl.combined;
    ssl_certificate_key /home/[mydomain]/domains/nextcloud.[mydomain].com/ssl.key;
    root /home/[mydomain]/domains/nextcloud.[mydomain].com/public_html;
    add_header X-Content-Type-Options nosniff;
    add_header X-XSS-Protection "1; mode=block";
    add_header X-Robots-Tag none;
    add_header X-Download-Options noopen;
    add_header X-Permitted-Cross-Domain-Policies none;
    add_header Referrer-Policy no-referrer;
    fastcgi_hide_header X-Powered-By;
    location = /robots.txt {
        allow all;
        log_not_found off;
        access_log off;
    }
    location = /.well-known/carddav {
        return 301 $scheme://$host:$server_port/remote.php/dav;
    }
    location = /.well-known/caldav {
        return 301 $scheme://$host:$server_port/remote.php/dav;
    }
    client_max_body_size 512M;
    fastcgi_buffers 64 4K;
    gzip on;
    gzip_vary on;
    gzip_comp_level 4;
    gzip_min_length 256;
    gzip_proxied expired no-cache no-store private no_last_modified no_etag auth;
    gzip_types application/atom+xml application/javascript application/json application/ld+json application/manifest+json application/rss+xml application/vnd.geo+json application/vnd.ms-fontobject application/x-font-ttf application/x-web-app-manifest+json application/xhtml+xml application/xml font/opentype image/bmp image/svg+xml image/x-icon text/cache-manifest text/css text/plain text/vcard text/vnd.rim.location.xloc text/vtt text/x-component text/x-cross-domain-policy;
    location / {
        rewrite ^ /index.php;
    }
    location ~ ^\/(?:build|tests|config|lib|3rdparty|templates|data)\/ {
        deny all;
    }
    location ~ ^\/(?:\.|autotest|occ|issue|indie|db_|console) {
        deny all;
    }
    location ~ ^\/(?:index|remote|public|cron|core\/ajax\/update|status|ocs\/v[12]|updater\/.+|oc[ms]-provider\/.+)\.php(?:$|\/) {
        fastcgi_split_path_info ^(.+?\.php)(\/.*|)$;
        set $path_info $fastcgi_path_info;
        try_files $fastcgi_script_name =404;
        include fastcgi_params;
        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
        fastcgi_param PATH_INFO $path_info;
        fastcgi_param HTTPS on;
        fastcgi_param modHeadersAvailable true;
        fastcgi_param front_controller_active true;
        fastcgi_pass localhost:[port];
        fastcgi_intercept_errors on;
        fastcgi_request_buffering off;
    }
    location ~ ^\/(?:updater|oc[ms]-provider)(?:$|\/) {
        try_files $uri/ =404;
        index index.php;
    }
    location ~ \.(?:css|js|woff2?|svg|gif|map)$ {
        try_files $uri /index.php$request_uri;
        add_header Cache-Control "public, max-age=15778463";
        add_header X-Content-Type-Options nosniff;
        add_header X-XSS-Protection "1; mode=block";
        add_header X-Robots-Tag none;
        add_header X-Download-Options noopen;
        add_header X-Permitted-Cross-Domain-Policies none;
        add_header Referrer-Policy no-referrer;
        access_log off;
    }
    location ~ \.(?:png|html|ttf|ico|jpg|jpeg|bcmap|mp4|webm)$ {
        try_files $uri /index.php$request_uri;
        access_log off;
    }