I just followed the step by step instructions, and the sync worked on the first try - thanks @feloneouscat !
2 comments just in case for others:
a) the comment about BACKSLASHES - I had to ponder a few times, but this is referring to the space character in the path "Mobile Documents", which in a terminal needs the backslash escape, "e\ D" in the path. I followed the instructions and did NOT add the backslash and all worked as described.
b) After creating the iCloud sync (from 1st MacBook Air M2 Ventura), I went to a fresh installation of Joplin on an older Intel mac (2015 MacPro Monterey), downloaded, followed the instructions above again (except I didn't make a copy of the empty .config/joplin-desktop), but I set the Synchronization target to File System with the same path, clicked sync, and my notes that I sent up to the cloud came down to my 2nd mac. I can also see notes syncing back and forth between both macs (at the timed interval as well as when I "Synchronize" manually).
Very nice - this syncing is also critical to my workflow (working on a laptop and desktop depending on in office or work-from-home).
I'm testing out Joplin to see if this may become my standard note taking app for typed notes. The syncing was essential so I was glad to find this very easy way to use iCloud.
I'm liking Joplin so far.