Thanks for creating a new forum topic, @tweakfreaks I can imagine how concerning it’s when you get a blank meta box after updating Yoast SEO to v20.9.
Can you please open the post edit screen and check if there are any JavaScript errors in the browser’s console? This help article explains how to check for JavaScript errors.
On the other hand, we often see problems occur in combination with another plugin or theme. The fastest way to rule out any conflict is to deactivate all non-Yoast plugins and switch to a standard theme like Twenty Twenty-Two.
Please test this on your development or staging site if you have one. If not, we recommend using the Health Check & Troubleshooting plugin. This plugin has a troubleshooting mode, which does not affect normal visitors to your site.
If you’re unfamiliar with checking for conflicts, we’d like to point you to a step-by-step guide that will walk you through the process: How to check for plugin conflicts
Let us know the results!