I was able to setup sync with my iCloud on iOS, and it works between my iPhone and iPad. I then setup iCloud sync with my Mac, and it is asking for “sync store name”. I put “devonthink”, and it syncs, but it seems to be in parallel with the iOS syncs; files are not syncing between the two systems.
You are setting up iCloud Drive (incorrect) instead of iCloud (correct). Select the iCloud Drive location and press the minus button to remove it. It is incompatible with DEVONthink To Go and iCloud sync has replaced it.
PS: I just tweeted about this. You should follow us on Twitter (@devontech).