There is an undocumented filter for the user field, most of the user field is not documented.
Anyway, there is a filter that you can use to alter the results for the user field, here is where it’s called in the user field code
$args = apply_filters("acf/fields/user/query", $args, $field, $options['post_id']);
$args = apply_filters("acf/fields/user/query/name={$field['_name']}", $args, $field, $options['post_id']);
$args = apply_filters("acf/fields/user/query/key={$field['key']}", $args, $field, $options['post_id']);
$args is the same as the arguments used in the WP function get_users(), https://developer.wordpress.org/reference/functions/get_users/
In your filter you would get the current user roles and then alter the arguments to include only other users with the same role, I think with the “role__in” argument, but I’m not sure.
Sorry I cannot be more specific, but I only know that the filter exists, I’ve never used it.
