The Cloud view lists every cloud storage folder on your Mac, one card per account: iCloud Drive, Google Drive, Dropbox, OneDrive and others. It shows how much is on this Mac and how much is online only.
Online only files
Online only files are not downloaded. They use no space on your Mac, so they never inflate the map and are never counted as reclaimable. A scan never opens them, so it never triggers a download.
Remove Downloads
For services that keep files on demand, Remove Downloads makes downloaded files online only again. It lists the files you have not opened in 90 days that are at least 10 MB, largest first. Removing downloads one location at a time is free; removing them in bulk is part of Pro. The files stay in the cloud and download again when you open them. This cannot be undone from Activity, and the review sheet says so.
Some services keep a full copy of every file in a normal folder. Removing downloads is not possible there. The card says so: to free space, remove files from the service or use its selective sync.
Two accounts and old folders
A cloud folder that is no longer connected, for example after you switched accounts, is marked Not connected. It often holds gigabytes of local copies. Part of this check reads the cloud apps’ own settings, which only the direct download can do.
Compare checks whether its files are in your current account by comparing their content. Files that are online only fall back to name and size and are marked Not verified. Compare is part of Pro.
Folders that show as unknown
Cloud folders in ~/Library/CloudStorage need permission to be read. See Full Disk Access.