This error indicates an issue with one of your active plugins, often related to the newsletter form functionality from WP Forms or other form plugins.
How to resolve the error:
1. Identify the plugin responsible for the newsletter form feature on your website.
2. Contact the developer or support team of that plugin for assistance.
3. While waiting for a response, consider temporary solutions such as disabling the plugin or using an alternative newsletter form solution if available.
It’s often because the plugin is not updated, so that it’s compatible with Block Themes.