screen-options-set_option.php

<?php
/**
 * Save the screen option setting.
 *
 * @param string $status The default value for the filter. Using anything other than false assumes you are handling saving the option.
 * @param string $option The option name.
 * @param array  $value  Whatever option you're setting.
 */
function set_option( $status, $option, $value ) {
	if ( isset( $_POST['wp_screen_options_nonce'] ) && wp_verify_nonce( sanitize_text_field( wp_unslash( $_POST['wp_screen_options_nonce'] ) ), 'wp_screen_options_nonce' ) ) {
		if ( 'wordpress_screen_options_demo_options' === $option ) {
			$value = isset( $_POST['wordpress_screen_options_demo'] ) && is_array( $_POST['wordpress_screen_options_demo'] ) ? $_POST['wordpress_screen_options_demo'] : []; // WPCS: Sanitization ok.
		}
	}

	return $value;
}