https://wpml.org/errata/wpforms-php-8x-issue-submitting-a-form-with-checkboxes-fields/
WPForms - PHP 8x - Issue submitting a form with checkbox fields - WPML
Mar 3, 2023 - If you have a form with checkboxes created with WPForms plugin running under a PHP 8x server, it won't work when you try to submit it. Instead you will
submitting a form