Where is icloud drive on the mac ssd and can I move it to an external ssd?

If the user is presently using iCloud and syncing files to iCloud.

Copies of this same files will also be on the computer.

That is so when an Internet Connection is not available, you can still work on the files.

Then when an Internet Connection is available, the changes will be up loaded to iCloud

Instead of trying to move or, as Previous Contributor suggested, Copy the files to an External Drive

Perhaps subscribing to iCloud+ plans and pricing could be an option

I'm curious as to where.

~/Library/Mobile Documents/ and in the hidden Desktop and Documents folders that still exist in your home.

iCloud is in the Cloud as the name implies. You can not 'move' it. You can however, COPY all the files from your iCloud drive to an external SSD drive if you like.