Duplicate CR3 files created on hard drive after import to LR CC.

Are you using Lightroom Cloudy or Lightroom Classic? The CC reference might indicate you are using the cloud version as that is the (now defunct) older name for it. Please post your precise version info as the answer to your question depends on it. Classic has separate modules called library, develop, etc. The cloud version has just one interface and no separate named modules but you can invoke the adjustment sliders at any time. The cloud version will always make a copy of your image when importing before uploading to the cloud. Then when it is uploaded to the cloud, by default it will delete the copy it made on your hard disk when you are not actually actively using the image. It will redownload a copy from the cloud when you need to. In Classic when you import, you get a choice whether to add (meaning it just uses the files in their current location), move (it moves the files to a different location for you), or to copy the files. Classic never uploads original images to the cloud. It can only upload reduced resolution previews to the cloud.

Please check your import options if you have the option "Make a second copy" enabled.

More about the import options you'll find here: How to specify import options in Lightroom Classic (adobe.com)