Hello again,
If you’re talking about making it so nobody can view “All Posts” in the wp-admin dashboard, but rather force them to view a specific category instead via PHP, that would be a change to core files in WordPress. I would recommend against that, but would instead suggest you use a Page Rule to add a 301 (or 302) redirect via .htaccess, or whatever method your host supports:
example.com/wp-admin/edit.php
-> example.com/wp-admin/edit.php?category_name=clients
This should work for .htaccess:
RedirectMatch 301 ^/wp-admin/edit\.php$ /wp-admin/edit.php?category_name=clients