People love blaming the theme 😉
There’s nothing in GP that limits anything like this, it’s actually a WordPress limit.
You can try adding something like this to your functions:
@ini_set( 'upload_max_size' , '64M' );
@ini_set( 'post_max_size', '64M');
@ini_set( 'max_execution_time', '300' );
Adding PHP: https://generatepress.com/knowledgebase/adding-php-functions/
However, adding images this big will be terrible for your load time/SEO.