In what scenarios would mod_alias not work in .htaccess for hiding a folder in a URL?
Mod_alias may not work in .htaccess for hiding a folder in a URL if the server configuration does not allow the use of mod_alias directives in .htaccess files. In this case, you can use mod_rewrite to achieve the same result by rewriting the URL to hide the folder.
RewriteEngine On
RewriteRule ^folder/(.*)$ /$1 [L]