We are also experiencing this. I reported it to Shopify Plus customer report and they asked me to reach out to Google instead. I did this and, as you would expect, they basically said that it’s a Shopify issue.
I’ve tried implementing the conversion as both a GTM “Google Ads Conversion Tracking” tag as well as an HTML tag, like in the original post.
What is confounding to me about this issue is that I don’t see any errors in the console from either tag approach though I do see the tags being rendered in the DOM. Instead, there is just a lack of the expected network requests to googleadservices.com and doubleclick.net.
Like @pashadev , we’re also going to workaround by implementing through Additional Scripts.