Your product title shouldn’t contain HTML code. Its role is more than just presentation on the product page: the title is used across countless places, like confirmation emails to customers, providing data to search engines, listing the products on the Shopify admin etc. Therefore it should strictly be plain text.
What I would recommend, if you wanted to adjust the presentation on the product page, is to use metafields to capture the different parts that make up your product title, then update your product page template to use these values when outputting the product title. That way you can fully customize the HTML markup to your liking while keeping the real product title intact.