See here: Cameras supported by Camera Raw
You need a newer version of Lightroom. Apparently 6.1 is enough (so 6.14 will do). As 6.X is the last perpetual license you still may be able to buy a version of that. Else you will need to take a Photography plan subscription or you need to use the free DNG converter to convert NEF files to DNG files.
Grazie per la risposta! (purtroppo non so nulla di inglese e rispondo in italiano). Sulla mia versione 5.7.1 mi dice di non esserci aggiornamenti di software. Dove posso trovare l'aggiornamento che dici di poter inserire??
Grazie ancora Maurizio
Version 5.7.1 was the final update for the 5.x version.
To get to the 6.x version, that requires a purchased "upgrade".
Since the current version of LR Classic is 8.0, getting the older versions is becoming harder.
You can answer in Italian. I use the translate feature, no problem. That's accurate enough to grab the sense of your writings.
See here on instruction on how to buy Lightroom 6: https://laurashoe.com/2017/10/19/where-to-buy-the-perpetual-version-lightroom-6/
It's still working for the moment. But Lightroom 6 is also End of Life and the version 6.14 is the last one.
When you buy the version 6, you need to upgrade to version 6.14 to get the latest cameras supported by Lr 6.
Just a last remark: the upgrade from 6 to 6.14 is free of charge...