There is an old (2010) $15 omnichord Kontakt library for this from Puremagnetik, call Ultrakord.
It also includes Ableton and Logic versions, around 120 meg each.
It comes with 9 .nki variants, and the deeper you know Kontakt, the more fun you’ll have.
Pressing a key strums one way, releasing it strums the opposite way.
To create useful chord-based song patterns from the parts, with the way they are laid out on the keyboard, you’ll want some little stickers you can apply to label the ones you’ll want to be playing, as they may be spread widely on the keyboard. When you press the Kontakt gui’s wrench icon upper-left of Kontakt gui, the full instrument control set appears. Using the Tune and Speed knobs helps dial in various candies. In the upper left of the expanded gui, by the word Source, there are two buttons, to choose among several ‘machines’, and some factory presets, altering playback accordingly, some of which are very interesting, some are noise. So taking notes and saving named presets will be lucky. Lots of effects are there to be added, amps, filters, stomps etc, and there will be 8 control dials for the instruments defaults.
There are also 30 or so loops in the ModulesUltrakord-Apple-Loops folder, to use or modify or combine as desired, again, the gui’s wrench icon opens up possibilities, that may vary a bit
as you try things out, not totally uniform or linear.
Well worth the price of a couple Starbucks and Carls Junior mood-modifiers.
If experiments find two items you want to combine, right-click the second one
and choose omni for midi to hear them. (apologies to Kontakt Masters, I am certainly not one, myself)
I do have full Kontakt 6, so don’t know it fares in the Kontakt player. The free Guitar Rig
version would certainly be useful for addon-effects throughout the pianobook.