Get Variable Values in View.xml

For better understanding please have a look this view

https://github.com/magento/magento2/blob/2.4.0/app/code/Magento/Catalog/etc/view.xml

with the following implementation

https://github.com/magento/magento2/blob/2.4.0/app/code/Magento/Catalog/Model/Product/Image/ParamsBuilder.php#L173

You can get the variables from etc/view.xml files in a couple of ways.

Let's assume we want to get the value of product_image_size from the Magento_Wishlist module... https://github.com/magento/magento2/blob/2.4.4/app/code/Magento/Wishlist/etc/view.xml

In a Template (.phtml) File

<?= $block->getVar('product_image_size', 'Magento_Wishlist') ?>

Remember to properly escape this output depending on how you are using it (not shown)

In a PHP Class

$this->viewConfig->getViewConfig()
    ->getVarValue('Magento_Wishlist', 'product_image_size');

Here is an example within a full custom block...

<?php
namespace YourNamespace\YourModule\Block;

use Magento\Framework\View\Element\Template;
use Magento\Framework\View\ConfigInterface;
use Magento\Framework\View\Element\Template\Context;

class YourBlock extends Template
{
    /**
     * @var ConfigInterface
     */
    protected $viewConfig;

    /**
     * Constructor
     *
     * @param Context $context
     * @param ConfigInterface $viewConfig
     * @param array $data
     */
    public function __construct(
        Template\Context $context,
        ConfigInterface $viewConfig,
        array $data = []
    ) {
        $this->viewConfig = $viewConfig;
        parent::__construct($context, $data);
    }

    /**
     * Get product_image_size
     *
     * @return int
     */
    public function getProductImageSize(): int
    {
        return (int) $this->viewConfig->getViewConfig()
            ->getVarValue('Magento_Wishlist', 'product_image_size');
    }
}