DNG converter for High Sierra 10.13.6

Camera Raw is a plugin for Photoshop and Bridge. It is not used by Lightroom. Instead, the Camera Raw engine is built into the Lightroom program. So to support later model cameras, you need to upgrade Lightroom itself.

Your version of Lightroom is too old to open those Raw files so, yes, you will need to convert to DNG then import into Lightroom.

The Nikon Z7 II is supported in Camera Raw 13.1 and Lightroom 10.1.

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

Unfortunately, Camera Raw 13 requires Mojave or later. See https://helpx.adobe.com/camera-raw/system-requirements/2021.html.  Camera Raw 12 was the last version which was compatible with High Sierra which won't read your Raw files.

This means you may not be able to have a Raw workflow with your current system unless you can upgrade your computer to OSX Mojave and install Camera Raw 13.

If you stay with your existing system, you'll probably have to use the Nikon software which came with your camera to open the Raw files and save them as TIFFs.