Where does turbotax keep my data on the hard drive - what folder? I don't just mean the PDF tax file output.

I question whether this is true.  It was true for years 2017 and earlier, when the extensions of these files were either .tax2017 or, going back even further, simply .tax.  But I can't find .tax2018 or .tax2019 files, even though I can open them in TurboTax (!).  To me it makes no sense.  This is how I happened upon this:

I sometimes want to create dummy returns, to see what might happen if input were different.  To do this I open up the "real" return and then immediately do a "save as" to a different name.  I can see these multiple files in my Documents/Turbotax folder for years prior to 2018.  Today I created a dummy file using this method, but I then decided I wanted to delete this dummy file.  As far as I can tell you can't delete a file from within Turbotax, so I went to the directory of the C drive to find the data file, where I planned to delete it, and I find that there are NO .tax2019 or .tax2018 files anywhere to be found.  (I did a global search.)  Can anyone explain what changed in 2018 and where this data is being saved?  I know that the file name which appears at the top of the screen in Turbotax shows a .tax2018 or .tax2019 extension but the file can't be found.  By the way, I've set my options to show hidden files, so that's not the problem.