Bought a house w/cash 2020 with but don't recall entering any information inTurboTax. What is the name of form I would have written info on to submit to the IRS?

The purchase of a personal residence is not reported on a tax return.

There is nothing to enter unless you paid property tax.  You do not have to enter anything about purchasing a house unless you are trying to deduct mortgage interest, loan origination fees or private mortgage insurance, or property tax paid.  if you paid any property tax in 2020 you can enter that in Federal>Deductions and Credits>Your Home>Property Taxes