Stop wordpress being active on a subdirectory within WordPress

All files and directories from the installed directory are considered to be under its control by WordPress. You can exclude a directory by adding an htaccess rule.

Exclude the subdirectory “my_subdirectory” from a WordPress root installed website

# BEGIN WordPress
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_URI} !^/my_subdirectory
RewriteRule . /index.php [L]
# END WordPress