Hello all and Happy New Year - 2022 
I have two MacBook Pros - one running Catalina OS (10.15.7) since it is an older one and a newer MacBook Pro running latest Monterey OS (12.0.1). I have installed the latest Arduino IDEs in both machines but my libraries and sketches are in the default document folder which is also uploaded and shared in iCloud. I am wondering if there are issues with using the same shared library and sketchbook folder from two different machines? I only use one IDE at a time and shut it down before I switch and open the IDE on the other.
There should not be any problem. I use only one Mac, but very often I open and edit Arduino library files with an external text editor with the Arduino IDE open and save changes just before compiling in the IDE. Never had any problem.
Preferences..., though, are saved locally. It is saved in ~/Library/Arduino15 in my machine. I guess the "15" corresponds to the first version I ever installed. The File>Open Recent menu is populated from there and will be different for either of your Macbooks. While in Preferences, sure to declare additional board managers in both machines.
The Arduino app scans the folder structure when you launch it, so if you add a folder to the "iCloud drive>Documents>Arduino" folder (or wherever your workspace is located), you will see it in the File>Sketchbook menu next time, and switching computers has no effect.
Have fun!