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We've been talking about how Google deals with HTML5 in terms of SEO and ranking since 2010. While there can be issues with some elements, for the most part, HTML5 is fine for Google.
Google's John Mueller summed it up on Twitter that if you are using HTML5, it makes sense to use it properly. Using HTML5 properly on your site won't have a downside to your SEO efforts. As if, you won't worse off using HTML5 properly than you would if you used it incorrectly. :)
Google will look at the HTML source and pick up the content where it can see it. So I'd recommend using the Fetch as Google tool in Search Console to make sure you understand what Google sees.
Here is John's tweets:
I don't think we use them at all. People tend to be quite creative when it comes to using HTML :-)
— John ☆.o(≧▽≦)o.☆ (@JohnMu) June 8, 2018
It certainly makes sense to use HTML5 properly if you can, there's no SEO downside to doing so :).
— John ☆.o(≧▽≦)o.☆ (@JohnMu) June 8, 2018
Forum discussion at Twitter.
