While e-filing my Michigan non-resident 2018 return, TurboTax said MI requires me to sign & mail a form. I clicked "Next", but don't know what form to sign/mail.

[Critter]

Save a PDF of the fed & state returns WITH the worksheets and review the filing instruction page ... do it quick since online access ends tomorrow ...

When you sign this onto your online account and land on the Tax Home web page, scroll down and click on Add a state.  This will take you back to the 2018 online tax return.

Click on Tax Tools on the left side of the online program screen.  Then click on Print Center.  Then click on Print, save or preview this year's return.