Hi @HDK ,
Yes, this is correct. Only manual collections can be used for the purpose of tax overrides. Please bear in mind that you can add numerous products to a collection at once through the bulk editor, and CSV files can also be used to add products to a collection in bulk.
While I recognise that these methods are not as fast as using an automated collection, they can help you add products to a manual collection faster than by simply adding them one-by-one.