Form 8453 is literally titled "U.S. Individual Income Tax Transmittal for an IRS e-file Return" and is used to submit forms that the IRS requires you to mail in even if you e-file. The IRS will never release coding for this form and other attachments that should be mailed in for TurboTax to add to the software. This is why the link provided by ChondelLO points to the answer that states that Form 8453 must be mailed.
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