The file name extension that TurboTax uses for 2020 tax return data files is .tax2020. The default location is \Documents\TurboTax, but you could save a tax return file anywhere. TurboTax does not save "interim" versions of a tax return, unless you save them yourself by using "Save as" with a different file name. At most TurboTax saves one backup copy of a return. The file name is the same as the primary name, with a tilde (~) at the beginning.
