Fatal error when updating to PHP 8

I just downloaded7updated to the newest Version of Catch Responsive Pro - 4.7.8 ... because I need to switch from PHP 7.4 to PHP 8 (or higher)  - but when I switch the PHP the Website crashes. I disabled all Plug-Ins - but it still crashed with PHP 8 - It only says 'There is a fatal error on your website' What else can I do to make the Theme run with PHP 8 ??? Thanks for any help! 'sandra