I’ve got this answer from the ACF-Support.
Thank you for your email.
I hate to be the bearer of bad news but the acf_register_block_type() function currently does not support the ‘anchor’ property. You can have a look at its documentation here https://www.advancedcustomfields.com/resources/acf_register_block_type/.
I hope this helps and kindly let me know how this goes :).
