This almost always comes from a plugin or theme that failed to update properly.
- Log in to cPanel and open File Manager, then go to public_html/wp-content.
- Rename the plugins folder to plugins-off. If the site returns, a plugin is the cause.
- Rename it back, then rename single plugin folders inside it one at a time to find the faulty one.
- If the site is still down, rename your active theme folder in wp-content/themes so WordPress falls back to a default theme.
Check How to see website errors in cPanel for the exact message. If you get stuck, open a Technical Support ticket and include the error text.
