Magento 2: GTM checkout event from Mini Cart – window.checkoutGTMData is undefined on checkout page

I’m trying to fire a Google Tag Manager (GTM) checkout event when a customer clicks the “Checkout” button in the Mini Cart on my Magento 2 store.

Goal:
To push a GTM checkout event with product and customer data to window.dataLayer on the checkout page after the user clicks the mini cart’s checkout button.

• Required Parameters to Push:

• email (text)

• product_id (int)

• product_name (text)

• produrl (text)

• category (text)

• price_mrp (int)

• price_selling (int)

• sku (text)

• payment_method (text)

• cart_total (int)

• discount_code (text)

• What I’ve Tried

Path: app/code/Vendor/GtmEvents/ViewModel/DataCollector.php

public function getQuoteProducts()
{
    $items = [];
    $quote = $this->checkoutSession->getQuote();
    foreach ($quote->getAllVisibleItems() as $item) {
        $product = $item->getProduct();
        $items[] = [
            'product_id' => (int)$product->getId(),
            'product_name' => $product->getName(),
            'produrl' => $product->getProductUrl(),
            'category' => implode(',', $product->getCategoryIds()),
            'price_mrp' => (int)$product->getPrice(),
            'price_selling' => (int)$item->getPrice(),
            'sku' => $product->getSku(),
        ];
    }
    return $items;
}