Magento 2.3.5 load main product image to preload it

i created a phtml file, called in the catalog_product_view.xml file (inside the head.additional reference block), where i want to preload the main product image, for Core Vitals purpose, for example:

<link rel="preload" as="image" href="<?= $block->escapeUrl($imageUrl) ?>"/>

where $imageUrl is:

$imageUrl = $block->getImageUrl();

But, the url (cached) of the product image is not retrieved. No errors, but, simply this:

<link rel="preload" as="image" href/>

So, how can i simply get in the correct way the main product image url (the main product image in the product page?)

Thanks, regards