Theme conflict with Php 8+

I don’t think this has anything to do with your theme. This would happen with any theme. To fix this make sure WP_DEBUG is set to false in your wp-config.php file.

https://www.ads-software.com/documentation/article/debugging-in-wordpress/

If that doesn’t work you could try adding the following to your wp-config.php:

ini_set('display_errors','Off');
ini_set('error_reporting', E_ALL );

Thank you, WP_DEBUG was set to false but with the two next lines ini_set i don’t have the error anymore.