1. Work out which mode the drive is in
Storage settings does not separate cloud caches from documents, so start in Finder. Each sync app marks files with a status: a cloud icon means the file lives online and takes no local space, a check mark or similar badge means a full copy is on the disk. A folder full of check marks is the reason the drive is large.
A disk scanner shows the actual local bytes per folder. On current macOS, apps built on Apple’s File Provider keep their local copies under a CloudStorage folder inside your Library, so that is where the size appears. Note the figure before changing anything so you can confirm the result.
2. Google Drive: stream instead of mirror
Google documents two modes. Mirrored files are always stored on your computer and in the cloud; streamed files are primarily stored in the cloud and made available offline only when you open them. Switch in Drive for desktop under Settings → Preferences → Folders from Drive → My Drive syncing options, and choose Stream files.
Streaming still keeps a local copy of anything you have opened, so the folder does not drop to zero. Google notes that shared files can fill a hard drive if you sync them even though they never count against your Google storage, which is worth checking if a shared drive is mirrored.
3. Dropbox: make folders online-only
Dropbox’s help page describes the step on Mac: open the Dropbox folder in Finder, right-click a file or folder, and choose Make online-only. An online-only file is stored in the cloud and does not take up storage on your computer; it still appears in Finder and downloads when you open it.
Selective sync is the older alternative and removes a folder from the Mac entirely while keeping it in your account. Dropbox’s troubleshooting page notes that Basic users can only make files online-only on the latest Dropbox for macOS built on File Provider, while selective sync works on every plan. If the menu item is missing, that is usually why.
4. OneDrive: use Free up space
Microsoft’s Files On-Demand page for Mac gives the step: right-click a file or folder in the OneDrive folder and choose Free up space. The item becomes online-only, shown with a cloud icon, and downloads when opened. Always Keep on This Device does the opposite and pins a full copy; a green check mark means a copy is currently on the disk.
Microsoft documents cases where a pinned item can exist both as a placeholder and as a cached copy, which is why measuring afterwards matters more than trusting the icon.
5. Measure again, and never delete inside a synced folder
After switching modes, rescan. Space returns as the app releases local copies, which can take a while for a large folder. Files you open afterwards come back down, so a working set of recent documents will always occupy some room.
Do not delete files inside a synced folder to save space: the deletion syncs to the cloud and to every other device. Use the app’s online-only or streaming controls instead. iCloud Drive has its own version of this behaviour, covered in the iCloud guide. ClearDisk shows these folders with allocated sizes so you can see which drive is holding the space, but it does not change sync settings and does not offer synced folders for removal.
References & further reading
These guides combine the linked official guidance with ClearDisk’s documented behavior. Your files and app settings determine the right next step.