How much free space needs to be available in order to download from iCloud Drive?
The current belief is that it starts complaining about free disk space somewhere around 20% left. So if you have 282 GB free and are trying to download 185 GB, that would leave 77 GB free, which is less than 20% of your 500 GB hard drive.

I don't believe there's anywhere that codifies what "low" means in this context, though, so I can't point you to an official source that says it's 20%.