Hello
I believe you have TWO options:
#1. Create a folder that doesn´t sync with iCloud Drive so whatever you toss in it, will stay only on that computer. Like the previous poster suggested. (actually the only folders that automatically sync through computers are Desktop and Documents).
So to do this, just go to your homefolder (the one that has the home icon and should be named after your user) and create a folder there, Name it whatever you want and it'll be like the non-syncing documents or whatever folder.
#2- Turn off automatic Documents and Desktop syncing through iCloud Drive altogether (you'd do this if you don't have enough iCloud Drive space for instance or if you just don't want to use iCloud Drive). You turn it off on the macbook you don't wanna share the info from (or in both keeping in mind the documents you create in one won't automatically sync and the optimize space option won't work either since it uses the auto syncing for that).
Try this and let me know how that goes:
- (Before trying this, do a back up of the iCloud enabled documents folder to a different location, because if I'm correct after this, that document folder will be empty.
- Open system preferences --> iCloud --> iCloud Drive Options...-->Documents Tab and uncheck the "Desktop & Documents Folders" and also uncheck the "Optimize Mac Storage" at the bottom of the window.
So depeding on your needs I share this two options.
Hope you solve your issue.
Cheers!