Can a theme cause the 'WordPress there is a critical error on this website' error, and how can I troubleshoot this?

Yes, themes can cause critical errors, especially if they are poorly coded or incompatible with the current WordPress version. To troubleshoot, access your website via FTP or your hosting control panel and rename the theme folder in `/wp-content/themes/`. This will force WordPress to use a default theme. If the error disappears, the theme is the issue. Consider updating, reinstalling, or switching themes.