I have tried working on a project in iCloud. It was an total train wreck, wouldn't recommend.
What happens is this:
You create a project in your iCloud folder on computer A and record into it. All closed files (finished recordings, closed project files) are uploaded to the Apple server. On computer B these files will download eventually (as quick as network bandwidth permits) and you can use them there. So all files are copied twice, through the internet. This can be quite slow, depending on your connection.
Also, file locations in iCloud aren't what they seem. There is no visible folder 'iCloud' on your computer with your stuff in it. Instead, it's a hidden folder with cryptic names inside Library/Application Support. Now, MacOS normally handles this for you in the background so you don't even notice, but if you are building and saving Sampler instruments to iCloud, the paths to the samples, which are written into the instrument, will end up pointing to invisible audio files in a hidden location on computer A. These Sampler instruments may work on computer A, but certainly won't on computer B. And trying to salvage these on computer A will be difficult since the used audio files are invisible (with a dot in front of the file names) so you either can't see them or break the Sampler instrument. In any case, much of the work you put into these Sampler instruments will be destroyed.