finder says "iCloud storage is full" but it isn't even close

What do you see at System Preferences/iCloud/Manage? If you add everything up and it isn't close to the amount of iCloud Storage you have, other people have posted similar problems and after contacting iCloud support, found it was a server problem. iCloud support reset everything. You may have to politely ask for a level 2 person.

If necessary contact iCloud Support. You may have to try twice.

iCloud Support

Try contacting iCloud Support using the link I posted above.