You won’t see that option in the element’s editor, it’s an option to activate WP’s custom field on post/page editor.
As your custom field is created by ACF, there’s no need to activate WP’s custom field option, and because ACF is activated, the WP default custom field won’t show, for more info: https://plugin-planet.com/fix-custom-fields-not-showing-wordpress/
Anyway, if the custom field is created and filled with a valid value, you should be able to enter the meta field name directly as the video shows.
If the value doesn’t show on front end, make sure to enable the REST API for your ACF fields:
https://www.advancedcustomfields.com/resources/wp-rest-api-integration/