Taking another crack at keyboard matrix scanning using the NRF52 PPI

is there a way to set an array of pin modes & watches like how I'm able to read an array of pins with digitalRead?

I'm afraid there isn't anything at the moment, no...

As you had done, COLS.forEach(col => pinMode(col, 'output')); would work pretty well though, or maybe: COLS.forEach(col => col.mode('output'));