I can't watch YouTube videos on safari

1. Clear History

    https://support.apple.com/guide/safari/clear-your-browsing-history-sfri47acf5d6/mac

     Please read the article before clearing history, this is like low a level resetting of Safari.

2. Clear all website data

    https://support.apple.com/guide/safari/manage-cookies-and-website-data-sfri11471/mac

3. Enable Develop menu, click Develop in the menu bar  and  then Empty Caches from the dropdown twice.

    https://support.apple.com/guide/safari/use-the-developer-tools-in-the-develop-menu-sfri20948/mac