15 minutes after posting I figured it out…
It’s added with javascript:
acf.registerConditionForFieldType('hasValue', 'custom_field_type_name_here');
I have read through most issue threads regarding this on both acf & gutenberg github and from what I can tell WP devs have not even confirmed they are working to supply the hook ACF team has requested as solution to this problem. I hope Elliot is communicating “behind the scenes” or working on another solution because just waiting for WP Devs to change something they don’t agree is a problem will take very very long. Gutenberg has hooks that could prevent post saving but in frontend only so any validation logic would have to be moved to javascript instead of php/backend as it currently works in acf. I would imagine at least the required fields validation logic could be moved to javascript instead of backend? Please fix asap :'(
