When I select Play Mode in Dorico 4, I’m seeing a not-very-tall minimal and not-editable sort-of version of a piano roll, but nothing like a real piano roll I see in (for example) Introduction to Play Mode in Dorico | Play Mode in Dorico - YouTube . R-click/L-click/everything I can think of is getting me nowhere.
That video is for Version 3.5. The PLAY window has been completely redesigned for Dorico 4 and is a little different from 3.5 and is also currently not finished - there are a few things that will be reinstated in the next month or two (somewhat of a guess).
However, there IS a lower zone piano roll which is resizable and this will show which ever track/instrument you have selected. Go to ‘Window’ and ‘Show Lower Zone’.
Here’s the video tutorial: PLAY mode in Dorico 4