Not Supported
Google Sites does not allow custom JavaScript. You cannot fire Meta Pixel events (fbq('track', ...)) on Google Sites pages.
What works: Google Sites has a built-in Google Analytics integration (Settings > Analytics) that tracks basic page views. No conversion events, no custom events, no pixel tracking.
If you need pixel event tracking, migrate to a platform that supports custom JavaScript: WordPress, Webflow, Squarespace, or any headless CMS with a custom frontend.