Custom field not saved - wordpress

Question

I try to add a custom user field to the user by using WPGraphQL. Therefore I tried to recreate the example in the official WPGraphQL documentation https://docs.wpgraphql.com/extending/fields/#register-fields-to-the-schema :
add_action('graphql_init', function () {
$hobbies = [
'type' => ['list_of' => 'String'],
'description' => __('Custom field for user mutations', 'your-textdomain'),
'resolve' => function ($user) {
$hobbies = get_user_meta($user->userId, 'hobbies', true);
return !empty($hobbies) ? $hobbies : [];
},
];
register_graphql_field('User', 'hobbies', $hobbies);
register_graphql_field('CreateUserInput', 'hobbies', $hobbies);
register_graphql_field('UpdateUserInput', 'hobbies', $hobbies);
});
I already changed the type from \WPGraphQL\Types::list_of( \WPGraphQL\Types::string() ) to ['list_of' => 'String'].
If I now execute the updateUser mutation my hobbies don't get updated. What am I dowing wrong?
Mutation:
mutation MyMutation {
__typename
updateUser(input: {clientMutationId: "tempId", id: "dXNlcjox", hobbies: ["football", "gaming"]}) {
clientMutationId
user {
hobbies
}
}
}
Output:
{
"data": {
"__typename": "RootMutation",
"updateUser": {
"clientMutationId": "tempId",
"user": {
"hobbies": []
}
}
}
}

Answer 1

Thanks to xadm, the only thing I forgot was to really mutate the field. I was a bit confused by the documentation, my fault. (I really am new to WPGraphQL btw)
Here's what has to be added:
add_action('graphql_user_object_mutation_update_additional_data', 'graphql_register_user_mutation', 10, 5);
function graphql_register_user_mutation($user_id, $input, $mutation_name, $context, $info)
{
if (isset($input['hobbies'])) {
// Consider other sanitization if necessary and validation such as which
// user role/capability should be able to insert this value, etc.
update_user_meta($user_id, 'hobbies', $input['hobbies']);
}
}