LR says my Harddrive is full when its not

This is not a definitive answer, but ever since macOS switched to the more advanced Apple File System (APFS), it has been difficult to nail down exactly how much free space is on a macOS APFS volume, and macOS and applications often report different numbers. This is partly because of differences in how purgeable and temporary files are counted, such as Time Machine local snapshots; and also how APFS treats space that can be shared by multiple volumes. On my own Mac, Photoshop, Lightroom, third party utilities, and macOS all report different amounts of free space, and the difference is up to 40GB. More info:

The Finder confuses with wildly inaccurate figures for available space

Free space on an APFS volume is an illusion

Explainer: Disk free space

That’s just an explanation of how this discrepancy can easily happen on macOS. I don’t have a good solution, only a couple things to try. One is, if you use Time Machine, after updating your latest backup, use Apple Disk Utility to delete Time Machine local snapshots.

Managing snapshots: how to stop them eating free space

View APFS snapshots in Disk Utility on Mac (Apple)

The other idea is just free up more space until Lightroom thinks there is enough free. I know that’s not a great answer, but it’s just another way to get there.

Macintosh HD and Cloud space are two different things. You should right click on the macintosh HD and select information. Then you'll see what's up on hd from where your error msg comes. Maybe you even have enough space on HD but you have to release all. It depends on what info says.