[j0hnik]

<ytd-button-renderer id="submit-button" class="style-scope ytd-commentbox style-primary" button-renderer="" is-paper-button="">
	<a class="yt-simple-endpoint style-scope ytd-button-renderer" tabindex="-1">
		<paper-button role="button" tabindex="0" animated="" aria-disabled="false" elevation="0" id="button" class="style-scope ytd-button-renderer style-primary" aria-label="Оставить комментарий" style="">
			<yt-formatted-string id="text" class="style-scope ytd-button-renderer style-primary">Оставить комментарий</yt-formatted-string>
		</paper-button>
	</a>
</ytd-button-renderer>


<script>
var open_submit_button = document.getElementById('submit-button');
var submit_button2 = open_submit_button.querySelector("yt-formatted-string");

	console.log(submit_button2);

</script>

работает вроде