Dell has not supported that particular printer for a very long time. Anything distributed in a Stuffit (.sit) archive format is certain to be very old, and probably no longer useful.
Please read Printer and scanner drivers for Mac - Apple Support and pay particular attention to the boxed note stating "This list is no longer updated."
Although macOS supports only AirPrint-compatible devices, all hope is not lost. If you can find a compatible AirPrint print server that supports that printer, you may be able to keep using it. Here is one such device, among other potential solutions: https://www.lantronix.com/products/xprintserver-office/.
Good news: according to https://www.lantronix.com/support/xprintserver-compatible-printer-lists/?v=ios&pb=Dell, your Dell 3100cn should work with it. Check with Lantronix to be sure though.
Similar devices are listed in that Apple Support document, under "AirPrint print servers."