What's wrong with slash?

Question

htaccess

The essence of the problem is as follows. In the html code, a link of the form <a href="/catalog/">Каталог</a>
I.e. when you navigate, the directory should be displayed at site.ru/catalog/ , but it gives a 404 error.
If you remove the last slash site.ru/catalog , then everything is displayed.

.htaccess

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

site.ru/catalog/


site.ru/catalog


PS: Don't pay attention to https