1) Remove php_flag from .htaccess in the package
2) define ("TEST",1); to define ("TEST",0); in config.php use config_extended.php
3) After DB dump from manual Installation Go to System -> Upgrade phplist and then again take a dump. Check the difference and add ('version', '...', 0, NULL),
4) We have configured the _index.php with our changes and we replace it at /admin/index.php for auto upgrade and the we revert the changes after the upgrade. Since version 3.3.3 we change $GLOBALS['require_login'] = 1; to $GLOBALS['require_login'] = 0;.

Please make sure the _index.php and index.php are updated in the package from the latest zip package /admin/index.php

5) Please edit your config file and change "mysql.inc" to "mysqli.inc" to avoid future PHP incompatibility
6) PHP REQUIREMENT LINK : https://resources.phplist.com/system/start ( Does not work on PHP 5.3 so we have kept min req 5.4. Check in next version )
7) When we check auto upgrade with debug=died on cpanel it is redirecting to blank page. This is happening because the script has written some javascript code with is hiding all response.
8) We have removed imap from the list of php requirement under info.xml as it is no more a part of PHP core. Also user faced an issue while upgrading phpList on PHP 8.4 :
https://www.php.net/manual/en/intro.imap.php / https://www.php.net/manual/en/migration84.removed-extensions.php