Unlike the Notion for iOS app, it is not possible to use the virtual keyboard in Notion 6 to enter MIDI in real-time. I will go ahead and move this over to the "Notion Feature Requests" section of Presonus Answers.
Thank you for the feature request.
If anyone else agrees or disagrees, then please vote it up, or down.
In agreement click on the little blue triangle pointing up.
In disagreement click on the little blue triangle pointing down.
The developers pay close attention to those that are voted on the most.
You are allowed one vote.
Just viewing and agreeing but not clicking on the vote does not help the issue.
Please click on one or the other.