I think it is possible to move current post data from the default table wp_postmeta to the custom table. But need a lot of code to do, you can try to use the public API update to do that. Please read more here https://docs.metabox.io/extensions/mb-custom-table/#update
After following this steps, I can see the values in the custom table. I can also see values as admin columns.
However, when I edit the post, field seems to be empty. ¿Some caching problem?
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