Error Since 4.5.7

PHP: 8.0
WordPress: 5.9.3

Getting this on a clients website, since the update to 4.5.7

Notice: spl_autoload_register(): Argument #2 ($do_throw) has been ignored, spl_autoload_register() will always throw in /public_html/wp-content/plugins/product-add-ons-woocommerce/index.php on line 35

Deprecated: Required parameter $chosen_shipping follows optional parameter $parcels_array in /public_html/wp-content/plugins/woo-order-splitter/inc/classes/WC_OS_Shipping.php on line 1603

Deprecated: Required parameter $total_shipping_cost follows optional parameter $parcels_array in /public_html/wp-content/plugins/woo-order-splitter/inc/classes/WC_OS_Shipping.php on line 1603

Fatal error: Uncaught TypeError: count(): Argument #1 ($value) must be of type Countable|array, null given in //public_html/wp-content/plugins/woo-order-splitter/inc/functions.php:6845 Stack trace: #0 //public_html/wp-includes/class-wp-hook.php(307): wc_os_front_scripts() #1 //public_html/wp-includes/class-wp-hook.php(331): WP_Hook->apply_filters() #2 //public_html/wp-includes/plugin.php(474): WP_Hook->do_action() #3 //public_html/wp-includes/script-loader.php(2115): do_action() #4 //public_html/wp-includes/class-wp-hook.php(307): wp_enqueue_scripts() #5 //public_html/wp-includes/class-wp-hook.php(331): WP_Hook->apply_filters() #6 //public_html/wp-includes/plugin.php(474): WP_Hook->do_action() #7 //public_html/wp-includes/general-template.php(3042): do_action() #8 //public_html/wp-content/themes/storefront/header.php(18): wp_head() #9 //public_html/wp-includes/template.php(770): require_once('/home/755894.cl...') #10 //public_html/wp-includes/template.php(716): load_template() #11 //public_html/wp-includes/general-template.php(48): locate_template() #12 //public_html/wp-content/themes/storefront/template-homepage.php(15): get_header() #13 //public_html/wp-includes/template-loader.php(106): include('/home/755894.cl...') #14 //public_html/wp-blog-header.php(19): require_once('/home/755894.cl...') #15 //public_html/index.php(17): require('/home/755894.cl...') #16 {main} thrown in //public_html/wp-content/plugins/woo-order-splitter/inc/functions.php on line 6845
There has been a critical error on this website.