That’s not true, you can most definitely set the page_title using an app proxy, and with app embed blocks you can add additional meta tags for SEO - As specifically stated in Shopify’s documentation https://shopify.dev/docs/apps/online-store/theme-app-extensions/extensions-framework#app-embed-blocks
I’m not massively familiar with app theme extensions and liquid myself, however, the issue appears to be with your last caption as you’re missing the opening capture tag, I’m not quite sure why you’re trying to insert script tags containing the page_title anyway..? The following example works to add the additional tags, however, the page_title capture does not work to change the page title. I imagine this is due to the block being rendered after the page_title has already been set. A workaround would be to set the page_title in your initial app proxy liquid response and not via the app embed block.
{% capture page_title %}
{% endcapture %}
{% capture page_description %}
{{description}}
{% endcapture %}
{% schema %}
{
“name”: “App Embed”,
“target”: “head”,
“settings”:
}
{% endschema %}