customized subject – Add CSS class to posts with sure meta key

I’m engaged on my header navigation and I need to underline the menu merchandise for sure circumstances.

I want to add a CSS class if

• the put up has the ID 21638, or
• the put up has the meta worth ‘bloom’

The meta worth is an ACF relationship subject.

<nav class="header-navigation">
<ul class="header-navigation__list">
    <li <?php if (is_single(21638)) or (metadata_exists('bloom') echo 'class="current-menu-item"' ?>><a href="<?php echo site_url('/labels/bloom') ?>">Bloom</a></li>
</ul>

I managed to resolve the put up ID half, however how do I add situation relating to meta worth?