I extended Magento_Catalog in a custom theme and added the following block:
<?xml version="1.0"?>
<page xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_configuration.xsd">
<body>
<referenceContainer name="product.info.main">
<block class="Magento\Framework\View\Element\Template" name="lvluplink" after="product.info.price" template="Magento_Catalog::customline.phtml" />
</referenceContainer>
</body>
</page>
the template:
<a class="primary action" href="https://google.com"><?= __('Custom Button') ?></a>
The link shows up in the store, but clicking the link does nothing. I am running Magento 2.3.4 in developer mode and have run:
bin/magento setup:upgrade
bin/magento setup:di:compile
bin/magento setup:static-content:deploy -f
bin/magento cache:clean
bin/magento cache:flush