How can I hide folder name from URL using .htaccess - .htaccess

Question

I have a website with the root folder 'www', but I put all php files including index.php in a sub-folder of root.
I wrote myself a .htaccess file to redirect, so if I input www.test.com, it will jump to www.test.com/folder and display the index.php.
Below it's my .htaccess which I put in the root.
RewriteEngine On
RewriteBase /
RewriteRule ^folder2 - [L]
#ignore folder2 in which I put important files, but no works for the website
RewriteCond %{REQUEST_URI} !^/folder(.*)
RewriteRule (.*) /folder/$1
Right now, I want to change the .htaccess file to reach these goals:
When I input www.test.com, jump to www.test.com/folder as usual, but display the url without folder.
All the pages in folder will display the url without folder name.
Such as
www.test.com/shop/page1 -> www.test.com/page1
I searched some of the scripts, but none of them works.

Answer 1

I've found this related question which answers to your problem. The snippet from the answer is (note: it's adjusted to your needs):
RewriteEngine On
RewriteBase /
RewriteCond %{THE_REQUEST} ^[A-Z]{3,}\s/+folder/([^\s]+) [NC]
RewriteRule ^ %1 [R=301,L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule (?!^folder/)^(.*)$ /folder/$1 [L,NC]
Reference: https://stackoverflow.com/a/18361995/3673491

Answer 2

You can use below code.
RewriteEngine On
RewriteBase /
RewriteRule ^/?$ /folder/ [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ /folder/$1 [L]

Answer 3

Based on your current rules. You can just make a slight adjustment.
RewriteEngine On
RewriteBase /
#ignore folder2 in which I put important files, but no works for the website
RewriteRule ^folder2/? - [L]
RewriteRule ^/?$ /folder/ [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ /folder/$1 [L]