The Nikon Z6 should be supported by now, as I think the camera went public somewhere in 2018.
Please tell us more about your operating system and version, the software and version. Please use EXACT version numbers. "Latest version" does not tell us that you really have the latest version and will no more be true at the next version level.
I will move this to the Photoshop Elements forum. You will get more targeted help there.
ABAMBO | Hard- and Software Engineer | Photographer
You can work with your PSE2018 after converting your NEF files to the DNG raw format. Download and install the latest DNGconverter program (free). It will convert a whole folder of NEF files to the DNG format that PSE2018 can read and edit. Needs a batch conversion, but same quality and free.