In this thread
I detail my experience using the Dorico lower zone in a separate window on a separate display in Windows. I found a lot of issues, including that it enters wrong notes on the main window while sounding them correctly. I’m guessing this is a hangover from the move to iPad which doesn’t support multiple windows. Except the special case you mention here which is side car. Daniel mentioned this use case to me last summer so I’m sure it’s meant to be supported, but is part of the cleanup that needs to happen with Play and the lower zone.
Anyhow keep an eye out, I found that this application isn’t ready for prime time yet.