I think you are wrong. According to the documentation for the acf_add_options_page() the post ID can also be any string – only the default ist 'options'.
$args = array(
...
/* (int|string) The '$post_id' to save/load data to/from. Can be set to a numeric post ID (123), or a string ('user_2').
Defaults to 'options'. Added in v5.2.7 */
'post_id' => 'options',
...
)
Since I also get the values in other situations (see the 2nd example where I get all color values for the radio field or the 3rd example where I get the value for the other field from the same options page), the code can not be so wrong.
Since the 'post-id' was introduced in v5.2.7 I always use this.
Sorry, but this is not the solution…
