Hi,
PHP obtains input variables from HTML forms (through GET and POST requests), as well as from any cookies enabled on a page. By default, the maximum number of input variables allowed for PHP scripts is set to 1000. You can change this amount by setting the max_input_vars directive in a .htaccess file. If it not changes, this means, that your hosting doesn´t support a change of php_value by the .htaccess file. Please contact your hosting service.
Or you can go to php.ini and change the max_input_vars value.
After the change, you go to Woocommerce -> System status -> check "PHP max_input_vars"
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Go back to the menu and try again.
Best regards,