This is not true since about 2008. All major browsers parse the HTML without waiting for synchronous <script> to load. https://developer.mozilla.org/en-US/docs/Glossary/speculativ...

If the <script> uses document.write() and what's written contains unbalanced tags, or if the document is modified in some other ways, then they re-parse but that combination is rare. This page explains what to avoid to ensure re-parsing doesn't happen (the rules may differ with other browsers): https://developer.mozilla.org/en-US/docs/Glossary/speculativ...