Although MIDI drag & drop cannot be done directly from DAW to Scaler 3, it can easily be done by saving MIDI on the computer, then drag & drop by using File Explorer.
Both MIDI and audio drag and drop work the same way.
Please see video.
First, in Reaper, second, in standalone. And this can be done in ANY section.
Please note that this must be done from File Explorer to either Scaler 3 standalone or plugin.