too long

I'm new to the Rewrite mod and have been looking over it for the last few days but I am still struggling to get this to work.

I already have a .htaccess file in the root directory that is forcing the secure version of the site and hiding extensions, so that https://www.example.com/help.php goes to https://www.example.com/help

My problem is my admin tool at https://www.example.com/admin

I'd like it to work so that a page like list.php appears as https://www.example.com/admin/list but no matter what I trial, it always either breaks or redirects to the root index file.

Here my root .htaccess file

FallbackResource /index.php

RewriteCond %{REQUEST_URI} !^/[0-9]+\..+\.cpaneldcv$
RewriteCond %{REQUEST_URI} !^/\.well-known/pki-validation/[A-F0-9]{32}\.txt(?:\ Comodo\ DCV)?$
RewriteEngine On 
RewriteCond %{SERVER_PORT} 80 
RewriteRule ^(.*)$ https://www.example.com/$1 [R=301,L]

RewriteEngine On
RewriteCond %{REQUEST_FILENAME}.php -f
RewriteCond %{REQUEST_URI} !/$
RewriteRule ^([^\.]+)$ $1.php [NC,L]

Can anyone help with what I should add to the admin directories .htaccess file, it's a Redhat server if that helps.

Thanks in advance for any help.