Media browser thumbnails not showing after upgrade from 2.8.4 to 3.0.4

[halftrainedharry]

It’s a known issue with MODX 3.0.4 and PHP 7.4.
Take a look at this topic:

MODX 2.8.6/3.0.4 + PHP 7.4 breaks thumbnails in the manager

Summary The version of phpThumb that comes with MODX 2.8.6 has a line of code that throws a fatal error in PHP 7.4. (The phpThumb library is used in the MODX manager to generate the thumbnails in the media browser and the preview for image TVs.) Step to fix the issue To fix the issue, remove the word mixed from this line in the file core/model/phpthumb/phpthumb.class.php Alternatively change the PHP version to at least 8.0. Related issue on Github Environment MODX 2.8.6-pl PHP 7.4