Have you added list column into document library or site column into document library?
For list column, you should go to SharePoint admin center -> More features -> Search -> Search Schema -> New Managed Property -> Click Queryable、Searchable and Retrievable, add the crawled property of the column as mapping.
For site column, you should go to SharePoint admin center -> More features -> Search -> Search Schema -> Check whether the managed property of the column is Queryable、Searchable and Retrievable.
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