iCloud & iCloud Photos · Storage Studio and iCloud
How do I find the biggest iCloud files taking space on my Mac?
Short answer: Open Storage Profile from the More menu (•••): Biggest space-users lists the files really using your disk, including downloaded iCloud files, each with a Free up button that makes it online-only in one tap.
Open Storage Studio's Storage Profile from the More menu (•••) and look at Biggest space-users. It lists the files genuinely taking up room on your disk — including downloaded iCloud files — and each iCloud file has a Free up button that makes it online-only in one tap.
In Finder you can also open iCloud Drive, switch to list view, show the Size column and sort by it, though Finder shows full sizes even for online-only files.
Online-only files never appear in Storage Profile's list, because they aren't using space on your Mac. See Free up for iCloud files.