menus and hook_graphql_compose_field_results_alter

Mm, menus go via GraphQL in a pretty standard way, they don't go vie the GQLC field producers.

'menu_links' loads via

    $registry->addFieldResolver('Menu', 'items',
      $builder->produce('menu_links')
        ->map('menu', $builder->fromParent())
      );

Which in the GraphQL producer is:

web/modules/contrib/graphql/src/Plugin/GraphQL/DataProducer/Menu/MenuLinks.php

That loads up the menu tree:

    $tree = $this->menuLinkTree->load($menu->id(), new MenuTreeParameters());

    $manipulators = [
      ['callable' => 'menu.default_tree_manipulators:checkAccess'],
      ['callable' => 'menu.default_tree_manipulators:generateIndexAndSort'],
    ];
// ... yadda yadda yadda

So I don't currently have a way to altering the field results, the menu fields in the schema tap direct into props via the graphql module.

What data were you looking to change?
Might signal how tricky what you're trying to do is