Yepp, as @BJG145 wrote, the Fingerer is there for creating monophonic notes by pressing combinations of keys, like e.g. with some breath instruments where you have to open and close several holes to get a certain pitch. Additionally it offers one key intervals (so you could have a key to add a fifth or a second to the currently playing ones.
I was using this to create layouts that allow to play over several octaves.
Some material can be found further down this thread: Eigenharp Pico first steps, DAW connection, etc - #21 by NothanUmber
If you want to recreate this and have questions I can try to help.
But you could e.g. also just have a semi-tone modifier key that allows to add accidentals to play some out of scale notes on a diatonic scale.
I haven’t experimented with the Strummer yet, but what you describe sounds like a task for it.
Here a great video from @gbevin where he uses the Strummer on Alpha to play it like a guitar:
