Apache .htaccess to NGINX RewriteRules Port

This should work for your case. Inspired from the solution available @ https://serversforhackers.com/c/nginx-php-in-subdirectory

Final config file:

server
{
  listen 80 default_server;
  listen [::]:80 default_server;

  root /var/www/html;

  # Add index.php to the list if you are using PHP
  index index.php index.html;

  server_name localhost;

  location /
  {
    try_files $uri $uri/ =404;
  }

  # pass PHP scripts to FastCGI server
  location ~ \.php$
  {
    include snippets/fastcgi-php.conf;
    #       # With php-fpm (or other unix sockets):
    fastcgi_pass unix:/var/run/php/php7.4-fpm.sock;
    #       # With php-cgi (or other tcp sockets):
    #       fastcgi_pass 127.0.0.1:9000;
  }

  # for the sub-directory
  location /subdirecory
  {
    alias /var/www/html/subdirectory; 
    try_files $uri $uri/ @subdirectory; # send all the request to @subdirectory tagged location

    location ~ \.php$
    {
      include snippets/fastcgi-php.conf;
      fastcgi_param SCRIPT_FILENAME $request_filename;
      fastcgi_pass unix:/var/run/php/php7.4-fpm.sock;
    }
  }

  location @subdirectory
  {
    rewrite /subdirectory/about$ /subdirectory/pages/about.php last;
    rewrite /subdirectory/privacy-policy$ /subdirectory/pages/privacy-policy.php last;
    rewrite /subdirectory/contact$ /subdirectory/pages/contact.php last;
    rewrite /subdirectory/page$ /subdirectory/pages/page.php last;
    rewrite /subdirectory/terms$ /subdirectory/pages/tos.php last;

    rewrite ^/subdirectory/sitemap-([0-9]+).xml$ /subdirectory/parts/sitemaps/sitemap-$1.xml last;

    rewrite ^/subdirectory/(.*)/(.*)/(.*)/(.*)/?$ /subdirectory/index.php?bank=$1&state=$2&district=$3&branch=$4 last;
    rewrite ^/subdirectory/(.*)/(.*)/(.*)/?$ /subdirectory/index.php?bank=$1&state=$2&district=$3 last;
    rewrite ^/subdirectory/(.*)/(.*)/?$ /subdirectory/index.php?bank=$1&state=$2 last;
    rewrite ^/subdirectory/(.*)/?$ /subdirectory/index.php?bank=$1 last;

  }

}

For any doubts kindly ask. Also, thanks to you for such a question, I got to learn something new since I am new too :P; Cheers !!