I'm the original poster, and just checked that it still works. I went through the initial phase of defining my current tax return. Got the What-If Worksheet on the screen, put a check mark next to "Copy Column 1 to Column 2", and then checked the Use 2018 Tax Rates in Column 2. For me, it works - both AGI and tax payable change in Column 2.
Did you get all the way through the initial phase? I don't know if it would matter, but did you save the return before using the What-If? Really can't think of what it could be.
