IMO that's an overstatement... It might refer to the current situation of JackRouter not being available on recent versions of macOS, while still being available on Windows. On Windows it only works for ASIO-enabled applications though, so that limits the applications that can take advantage of it. There are also "virtual soundcard" drivers available for both platforms.
Both SuperCollider and SonoBus can use ASIO, you can try using Jack to route the audio from one to another.
- Install Jack2 (I think the current version is 1.9.17)
- make sure to include JackRouter when installing
- start Jack in QJackCtl (using ASIO backend preferably)
- start SuperCollider and SonoBus, set both to use JackRouter as the audio device
- make/change the connections in QJackCtl
Disclaimer: I haven't tried this configuration myself. Also - with Jack, particularly on Windows, you might encounter various issues, so be ready for a potentially "bumpy ride" setting it up...
Marcin