Yes; thanks, Jean, for replying and for confirming the reason! I stumbled over the answer last night while reading through the IRS instructions for the 1040 SR, seeing the worksheet for "Qualified Dividends and Capital Gains", and filling it out with the appropriate amounts. QD + CG > Line 15, and, as they are taxed at 0 % at my 2020 level of income (after backing out a lot of the SS received), the resulting amount for Line 16 = 0. I think my initial "freak-out" was primarily due to never having been in a situation before where I have not paid some amount of income tax! As a suggestion, it might be nice if Turbo Tax added pertinent worksheets to the final printout; that would have helped me better understand what was going on behind the scene in the calculations. Otherwise, very happy with the way Turbo Tax works; it saves a lot of time.
Best regards,
David