Sorry ... but if you don't currently have the 2017and prior on your computer now it is too late to download them as TT doesn't support them. Upgrading to OS 11 will not make the older programs unusable ... check by opening the currently installed programs.
Now you should always save the return as a PDF (with and without the worksheets) for future reference when the program is no longer available. Yes it is not the same but it is better than nothing.
TT has only supported the years still open to file for a refund so right now that is the 2018 - 2021. This has always been the rule and it will not be changing so if your computer loses the program files they can no longer be downloaded or updated thus it is important to keep the PDF files which do not need the active program to read.
