Hi @andyguzman,
Thank you for reaching out. The ACF control should display a dropdown that allows you to select any ACF field that has been created, broken down by the field group that the field is in. You should not be able to select the field groups directly.
However, it sounds like you might be using the “Group” field type, which then supports sub-fields. If so, you are correct, Block Visibility does not currently allow you to choose sub-fields within a “Group” field type. You can only choose from top-level fields.
That said, you can use the Metadata control as you described. The control is fairly basic, but it works well for text-based fields. You would just set the meta key to field_group_field_name.
Please let me know if I can answer any additional questions.
Best,
Nick