my 2018 tax file ext is *.tax 2019 desktop program wants *.tax2018.....what gives???

If you used Turbo Tax 2018 to create your return, it will create a *.2018 file.  Did you run Turbo Tax 2019 to start a 2019 return?  I would do a search on all the *.tax* files in your document folder to make sure you are loading the right one. 

2019 would only want .tax2018 for transferring certain data from te 2018 return.   are you sure the program you opened was TT for 2019 and not 2018,  each year is a separate program.