My state return shows a line 28 of 'TOTAL PAYMENT DUE. See the Instructions.' There are no TurboTax provided instructions in order to pay my PA taxes. How can I then pay?

When you print out the PA forms, TurboTax will include a cover letter detailing how and where to pay.  You can also get this by clicking on "Preview File Printing" before you print it out.    If you're E-Filing, you can also select a preview copy to view.  It includes the cover letter.

You are correct for all past years [2012 - 2019], but for this year [2020], no such provided instructions are provided. I know: I've printed out the PA tax forms.

From the PA Dept. or Revenue website:

PA Department of Revenue

Payment Enclosed

1 Revenue Place

Harrisburg, PA  [social security number removed]

In the FILE tab you can choose your option on how to pay the state ... if you choose to mail in a check then the mailing instructions should be included in the PDF with the WORKSHEETS in the Print Center.