iCloud Drive not syncing after macOS re-install
After several comments and clarifications, the iCloud sync process did eventually start.  It took about 12 hours of leaving the laptop plugged-in and awake for the syncing to start.

Because there's no UI (this is supposed to be a background process), you really have no good way to measure the progress.  Unfortunately, this has been a knock against iCloud for many years and Apple doesn't appear to be making any changes to improve in that area.