Override the page title with a value from an API response

I built a custom Drupal module. The module fetches data from a 3rd-party API and builds a block. I need to use a value from the API response to override the title (and head_title) of the page that the block is placed on.

I tried saving the value to the node in the Block controller:

$node = $this->getContextValue('node');
$node->page_title_override = $apiValue;

And then using that from hook_preprocess_html().

function myModule_preprocess_html(&$variables) {
  $pageTitleOverride = $node->page_title_override;
  $variables['head_title']['title'] = $pageTitleOverride;
}

It appears that the preprocess hook executes before the block controller, so $pageTitleOverride is empty.

Do you have any idea on a better approach?

You are saving the value to the node in the Block controller only temporary, but blocks are not necessarily rendered in the same request. The block could have been cached a long time ago before the page is built or, if the block is not cacheable, it can be cached in the page as a placeholder so that the preprocess hook runs in a later request.

So what you can do depends on how cacheable the block and the title are. The module metatag provides more tools to set the page title dynamically, either through attached html_head metadata or tokens.