Install PHP file manager for TinyMCE 5 and 4 by including PHP files
Download the files of Flmngr file manager
Download the latest version of PHP version of Flmngr, then unpack it to some folder inside your website structure.
The location of where you unpack the files will affect to File Manager URL parameter you will specify later. For example, if you unpack to
/var/www/flmngr, the URL of File Manager will probably be