Cannot get the reason for Recalculate style - Chrome devtols

This screenshot below shows recalculate style event log at 1391 ms. I am trying to reverse engineer to track it source. However Initiator reveals nothing when clicked on it. This is a production site of course.

Second, I want to draw attention to videoseries(youtube.com) entry in network waterfall ( blue colour belt ). This is iframe with lazy load firing much before LCP and in fact load event. Load event occurs after the last waterfall entry of fetch-pollyfill in yellow. Now, my question is that why lazy load when I can call it in parallel with questionSlug script in yellow at the top?

Related concern to sequence of loading -:

Let me share another screenshot(localhost this time) with FCP and Load event markings

Now, there is script of adsbygoogle.com declared as

<script data-ad-client="ca-xxx-xxxxx" src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script>

On localhost, I tried to not defer it yet the outcome is same in waterfall as is on first screenshot from production panel which brings to my third question. Wouldn't it be better if this would have been fired in parallel as well to shrink the load event and LCP? How can I do that?

There are multiple questions and I understand. Hopefully you will see the effort that goes into putting into a question. Thanks!