I Googled RUT-25. it's not an income tax form so Turbotax would never ask about it. it's a form to register or titling in Illinois a vehicle purchased out of state. The title / state registration wouldn't be issue until the form is filed. if Illinois is your domicile, it should have been registered. if not, how have you renewed the plates every year? Because the form is prenumbered it is not obtainable through the web
If you recently purchased and have not titled or registered the vehicle you are bringing into Illinois, you must complete a tax form. If purchased from a dealer, you must complete Tax Form RUT-25. If purchased from an individual, you must complete Tax Form RUT-50. One of these forms must be presented with a separate tax payment made out to the Illinois Department of Revenue at the time you apply for Title and Registration.
see the link for how to obtain the form. as to what it may cost. there would be the use tax, penalties and interest for late filing or type RUT-25 in the search bar in your browser.
https://www.pdffiller.com/jsfiller-desk10/?traceparent=00-764d50d15fda1d975f66cbd88b9cce4b-989b570e8...
