1) Do not delete [[site_name]] from table [[dbprefix]]site_content, keep as it is added to show some content on enduser page. (Not needed since 2.5.0-pl since default content is added by default)
2) The password encryption method has been changed so 3 files 'modhashing.class.php', 'modpbkdf2.class.php' and 'xpdo.class.php' are included in the install.php ( This files are not required in install.php from 2.7.0 but we need it for edit.php)
3) Do not change this files 'modhashing.class.php', 'modpbkdf2.class.php', 'xpdo.class.php'.
4) Do not change "background-image: url(data:image/png;base64," in table [[dbprefix]]site_templates since these are images encoded in base64. Let it be as it is. Since 2.5.0pl.
5) PHP REQUIREMENT LINK: https://modx.com/download and /core/vendor/composer/platform_check.php(Composer Dependencies require PHP 7.4.0)
6) Give writable permission to manager and root folder to check config.core.php changes.
7)Before MySQL 5.6 Full-Text table type is supported only with MyISAM Engine(Full-Text table type required by MODX), hence removed the innodb engine, default engine will be assigned automatically
8) Languages have been removed since 3.0.1-pl User needs to change languages from Toggle option from admin menu.
https://docs.modx.com/3.x/en/getting-started/upgrading-to-3.0/manager-language
9) Check and Move /manager/assets/ext3/adapter/jquery/ext-jquery-adapter-debug.js /manager/assets/ext3/adapter/prototype/ext-prototype-adapter-debug.js /manager/assets/ext3/adapter/yui/ext-yui-adapter-debug.js manual to original zip.