'How do I install plugins in Roundcube 1.5.2, which is integrated into ISPmanager 5 Lite?

I'm trying to install plugins according to the instructions for Roundcube via Composer in /usr/share/roundcube/. When the download and installation process ends, a message is displayed asking if this package needs to be activated. I enter yes, after which an entry in the file is recorded config.inc.php

$config['plugins'] = [
    'twofactor_gauthenticator',
    'html5_notifier',
    'quota',
    'contextmenu',
];

New menu items for these plugins do not appear in the web interface. I haven't been familiar with Roundcube before, are there any special features? Is there some kind of hidden admin panel for the administrator with settings? How do I configure and add plugins?



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