Nikon Z6 II RAW file not recognized

Adobe Photoshop Elements 2021 shipped with Adobe Camera Raw 12.3 and this got updated to 13.0 in November 2020. Unfortunately Z6 II Raw files need Adobe Camera Raw 13.1 and that's not available yet for Photoshop Elements.

For now, you'll need to convert Z6 II Raw files to the DNG format using Adobe's DNG Converter 13.1 before you can open them in Photoshop Elements.
Here's the download links:

DNG Converter 13.1 (Win)

DNG Converter 13.1 (Mac)

Please post Photoshop Elements related queries over at

https://community.adobe.com/t5/photoshop-elements/bd-p/photoshop-elements?page=1&sort=latest_replies&filter=all

Please see for yourself which version of Camera Raw supports a camera and which version of Photoshop is compatible with that ACR version: 

https://helpx.adobe.com/camera-raw/kb/camera-raw-plug-supported-cameras.html

https://helpx.adobe.com/x-productkb/global/camera-raw-compatible-applications.html

If your ACR version should support the camera the issue might be with the connection; try copying the files to a local volume before opening them.