Why headings matter
Headings are the page's table of contents. Readers skim them to find their part, screen readers use them to jump around, and search engines and AI assistants use them to understand what each section covers.
A good outline has one H1 that says what the page is, H2s for the main sections, and H3s inside those. Skipping from H2 to H4 does not break anything, but it usually means a heading was chosen for its size rather than its meaning.
Questions
Can a page have more than one H1?
HTML allows it and Google says it copes, but one H1 is clearer for readers and tools.
Should the H1 match the title tag?
They should say the same thing; they do not have to be identical. The title can include the brand; the H1 usually does not.
Does the checker see headings added by JavaScript?
No. It reads the HTML the server returns, as many crawlers do.
Is styling text bold the same as a heading?
No. Only h1 to h6 elements are headings to browsers, assistive tech and search engines.