low disc space but everything is in the cloud

How are you using iCloud on your Mac?

I am asking, because subscribing to iCloud Storage will not automatically move all your documents and data from your Mac to iCloud. You have to tell the system what you want to sync with iCloud.

• For example, if you want your Photos Library in iCloud, enable iCloud Photos.
• Or, if you want your Desktop and Documents folder in iCloud, enable Desktop&Documents.
• Look at the list of applications in the System Preferences > iCloud to see, which applications are enabled to store their documents and data in iCloud.

All other items will remain stored local, unless you drag them to iCloud Drive.

All items you are storing in iCloud will still take up storage on your Mac, as iCloud is primarily a syncing service, and it is keeping the local content on all your synced devices identical to the content of iCloud. See: iCloud Drive FAQ - Apple Support

If you want to save storage, enable "Optimise Mac Storage" and iCloud will remove the local copies for some of the older documents and data from iCloud Drive and your Photos Library, to free some storage. But it will not free all storage - iCloud Drive will try to keep the frequently used items cached locally, as space permits, so they will be immediately available and do not need to be downloaded every time you want to use them.

Optimise Storage should suffice to solve your storage problem, unless you have so many items in iCloud, that the local storage does not even suffice for the optimised smaller versions.

"low disc space but everything is in the cloud If all my stuff is in iCloud...and I just bought 4x more storage, why is my system still showing low disc space? Thank you"

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What's on the disk is on the disk. What's in iCloud is in iCloud.

So,...

Start with a Backup:

I. Backing Up: Be certain to create a backup of your Mac prior to perfuming all of this. That way, you can have something to restore from the Mac from, should anything go wrong with the iCloud Sync.

Once Backed Up:

II. Enable iCloud Usage: Enable as desired to be uploaded though iCloud, and give it a few to sync.

1. Open: System Preferences
2. Click: Apple ID (Top iTem)
3. Check Off: What is desired

Once Uploaded:

III. Delete the items from your Mac. Note that the items will remain on your Mac, until it is deleted. So, Abe gentian you backup your Mac first, as mentioned in step I.

See the thread https://discussions.apple.com/thread/251789307

Possibility of disk is malfunctioning repair the disk permissions Repair a storage device in Disk Utility on Mac - Apple Support

If you have problems with your Mac disk - Apple Support

If a disk can’t be repaired - Apple Support