Boldened Headings And Subheadings Can Get You A Google Penalty
You might be tempted to but boldening your H1 heading as well as your H2, H3, H4, and other subheadings will get you a Google penalty.
As headings must contain your target keywords or related ones to inform search engines what your content is all about and if you do bolden them that will include also the keywords . If Google ranked you higher based on those things, then that would encourage black hat SEO (pages full of bold and header tags) at the expense of content.
Plus, boldening the headings will make it look spammy and old school. People will get the idea they have been or are being marketed to when they land on a page that has the keyword emboldened.
Another thing to consider that it is an easier factor for Google to take into account when checking a page for SEO over-optimization.