We've upgraded from Moodle 3.3.2 to Moodle 3.8.2+ in our testing environment previously upgrading from Moodle 3.3.2 to Moodle 3.6.2. and, after verifying the system, to Moodle 3.8.2.+.

Having all the tasks finished and the system working, we've realised that in 3.8.2. the option "install plug-ins"  doesn't appear.  I attach document with screenshot of 3.8.2 and 3.3.2.

We have found out how to solve the problem temporarily.  Until now, for security reason, we used to change the default path "/admin" into "/<Project-admin" so as nobody could infere the administration path in Moodle.  However, this change that was possible without problems in previous versions, in Moodle 3.8.2+ prevents Moodle from finding the admin tools and as a result, Moodle 3.8.2+ doesn't allow plug-ins to be installed.

Once we have changed it to the default path, installation has gone well, but we’d like to change it as we used to do it in the previous versions.

The fact is that in Moodle documentation, you point out it's possible to do that change:

 //=========================================================================

// 5. DIRECTORY LOCATION  (most people can just ignore this setting)

//=========================================================================

// A very few webhosts use /admin as a special URL for you to access a

// control panel or something.  Unfortunately this conflicts with the

// standard location for the Moodle admin pages.  You can work around this

// by renaming the admin directory in your installation, and putting that

// new name here.  eg "moodleadmin".  This should fix all admin links in Moodle.

// After any change you need to visit your new admin directory

// and purge all caches.

$CFG->admin = 'admin';

We look forward to receiving your news.

Thanks in advance!