According to these guys you need to
... mark (Cmd/Ctrl + A) them in Lr CC, then right click and choose "Save To" - in the dialog choose the file format (Original and Settings) and chose location. Then add the local files to your Lr CC desktop catalog
if you want to move an actual set of images to your local computer.
Lightroom Classic CC is already behaving that way. A few important things to note:
You can only ever set up one catalogue to sync with Lightroom CC
It won't sync the full catalogue, you need to specify collections which you want to sync
The synced smart previews don't count towards the cloud storage usage, only full-resolution images do
If you import ...