Which machine? If its a modern apple notebook it is probably just the (at this point, standard failure of the) keyboard, and just a coincidence that it's started to happen the same time as your macOS update.
For what it is worth, my I key works fine on my 2015 running the most recent macOS.
You will hardly find anybody who will not agree with throAU that updates do not cause malfunctions in keyboards.Late 2012 rMBP.
Never had any issues whatsoever with the keyboard until the latest update.
Alternatively, try to boot from USB with another OS to confirm whether or not the I key works there.