Hi Tim,
The error message indicates an issue with the sortable function in the postbox.min.js file, a core WordPress file responsible for managing the post editor interface.
One possible cause of this error could be a conflict with a plugin or theme interfering with the function. Another possible cause could be a corrupted or outdated file.
Here are a few steps that you can try to resolve the issue:
1. Deactivate all plugins and activate them individually to identify if there is a plugin conflict.
2. Switch to a default WordPress theme, such as Twenty Twenty-One, and see if the issue persists.
3. Clear your browser cache and cookies.
4. Try updating WordPress to the latest version.
If you’re uncomfortable troubleshooting the issue yourself, you can also consider contacting your hosting support team, who can assist you further.
Let me know how it goes