Alt+B toggles the Virtual MIDI Keyboard window, or Option+B on Mac.
Assuming a US QWERTY keyboard layout or something similar to it, here's what does what when the virtual MIDI keyboard window is shown.

Z through Comma plays an octave of white notes.
S D, G H J, L are the accompanying octave of black notes.
Q through I plays the next octave above of white notes, with O and P tacking a lil' extra reach on the upper end.
2 3, 5 6 7, 9 plays the accompanying next octave of black notes, with 0 being accompanying extra reach for O and P on the row below.
Left and right arrows switch octaves down and up respectively.
Up and down arrows increase and decrease the MIDI channel notes will be sent on respectively. Beware, this wraps.

You can check and change the center note and MIDI channel by tabbing through controls in the window, or Shift+Tabbing to go back.
There are a couple of check boxes, you'll need to use a virtual mouse click to toggle those. I considered asking Cockos to make space work on them, but then we wouldn't be able to play.stop/pause the project in those tab order positions. Didn't seem worth the trade.

If the track you're playing notes on is armed, OSARA can provide feedback on the notes you're pressing, just enable Shortcut Help with F12 when the virtual MIDI keyboard is shown and start plonking a pretty ditty.
OSARA can't do the same for arrows yet. I've opened a feature request for that over on GitHub. Let's see if anything can be done.

Hope that helps!

Scott

Last update: 19th March 2025.