MIDI arpeggiator

Use JS Midi Arpeggiator before virtual instrumental.^[ Creating a MIDI Arpeggiator in REAPER]

Kontakt also has a built-in arpeggiator. Click the wrench, Script Editor, Preset > Factory > Sequencing > Arpeggiator.^[ Kontakt: Add an Arpeggiator to Anything - And Command it with Ease]