Your camera requires ACR version 11. Elements 2018 is only compatible with ACR version 10.3.
You can either upgrade to Elements 2020 which has ACR 12 or else convert your NEF files to DNG, using the free Adobe DNG Converter which can change the format in batches.
If you decide to go the upgrade route, you may want to wait a month or two, as, in recent years, Elements comes out with a new version around October. In the meantime, you can download a 30 day free trial of Elements 2020.