How to free up space on Macbook Air for iOS update By keeping files only in iCloud?
Yes - when you untick the check mark for Photos or Documents (likely the two largest items of iCloud space) you are asked if you want to keep a local copy (which you _don’t want to do) or just let the items live in the cloud (which you want - at least temporarily).

Choose to delete the local copy and then you will have the files only in iCloud.

Keep in mind, that after you delete files, macOS will keep space allocated / file content around for a short time as local snapshots or local time machine backups, so you will want to either thin the local snapshots or wait a day for them to age out.


Why does my mac not have free space even after I delete files?


Worst case - you can get an application like Daisy Disk (paid on the App Store, but a free trial from their web site - which has the bonus feature of letting you run a scan as administrator) and it makes it very simple to purge these temporary files sooner if you need. The app also does an amazing job showing you other large uses of space if my guess is wrong about documents and photos being your major space allocations.