The changed files did also the trick to restore our website. Our site was running on PHP 7.4 anyways, that was not the issue for our site.
We also used this short code snippet in functions.php to remove Google Fonts (german DSGVO nightmare):
https://gist.github.com/yanknudtskov/8246a8996b0529ffdf3ade5cef894b7d

Obviously the following line does not work anymore in 5.3 and breaks execution:
$avia->style->print_extra_output = false;

Any documentation/fix for what has changed that dramatically?

• This reply was modified 2 years ago by gejos.