We’re sorry to hear you are experiencing this issue on your site.
We understand you’re getting an error in Google Search Console saying Missing field “mainEntity”.
This looks like an issue specific to the recent changes to the FAQ schema markup that we have already fixed as of the version 15.9.1 release of the Yoast SEO plugin. If you haven’t updated the Yoast SEO plugin to the latest version yet, please update the plugin immediately.
Once you have the latest version of the Yoast plugin, the relevant error will disappear automatically from Google Search Console once Google detects the relevant changes on your website.
Updating immediately solves the problem with the FAQ schema, but it may take Google some time to recrawl your pages and remove the warnings.
To encourage Google to update to the latest version, you can use the Request Indexing tool in the Google Search Console. We have more details in this guide: How to update information in Google search results.