TurboTax for 1998 is no longer available. Even if you could find a copy, it probably would not run under any current Windows or Mac version. And even if it did run, it would likely be a preliminary version, without the final updates, and there is no way to update it.
If you just need to see a copy of the tax return, you could try using TaxPrinter. You send them your .tax file and they send you back a PDF of the tax return, which you can then view or print with Acrobat Reader. But the FAQ on the TaxPrinter web site says "TurboTax 1998 and 2002 will only print the tax summary." TaxPrinter has no connection with TurboTax. I have never used TaxPrinter, so I cannot make a recommendation. I'm just making you aware of it.
EDIT: Revised statement about TurboTax 1998 from the TaxPrinter web site.
If you used online for 1998, that tax return is long gone. TurboTax and the IRS save returns for seven years. If you used the desktop software on your own computer, then you need a pdf copy of the file; the tax file can only be opened using the software--which you will not be able to use on a newer computer in 2023. Why do you want a 1998 tax return?
the 1998 app is no longer avaialble from Turbotax and is not supported. you can buy old CD's from the internet. your problems are there's no licnese, it can't be updated, no state programs are available, and we can't even say that if you got the app it could be installed on your computer. (incompatable OS). neither Turbotax nor THE IRS retain copies of returns going back that far. if you have the XXXX.tax1998 file it can be sent to a website like taxprinter and for a fee they'll send you a printout. we don't vouch for them, but others have used them with no complaints