Hi there,
looks like that plugin doesn’t enqueue jQuery, which it should do seeing as it requires it.
Unless you use the Sticky Navigation GP doesn’t load jQuery either as it doesn’t require it.
You can force the them to load it with this snippet:
add_action( 'wp_enqueue_scripts', function() {
wp_enqueue_script( 'jquery' );
} );
https://docs.generatepress.com/article/adding-php/
If that doesn’t solve it then i would need to see the Site to debug.