How to block from domain access to dir with htaccess?

Using apache, creating a .htaccess file like the one below in the directory you want to hide should work.

Options +FollowSymLinks +Indexes -MultiViews
# Turn mod_rewrite on
RewriteEngine On
RewriteBase /files/videos/

# if the request is not for 127.0.0.1 then block it
RewriteCond %{HTTP_HOST} !^127\.0\.0\.1$ [NC]
RewriteRule ^ - [F]

Replace /files/videos with the path to your folder and 127.0.0.1 and 127.0.0.1 with your droplet’s IP address. This should refuse requests from anything using a domain and will only allow requests using the IP address directly.