Finding out which is it is a job for a mechanic. They have diagnostic techniques. it might be a wet and dry compression test for the rings and a bor-o-scope check for the valve stems.
I would hit up the KIA forums to see if someone successfully stopped oil consumption after it started.
Many moons ago I use to heat about Maxlife doing that very well. Now with all the high mileage oils on the market, they might be worth a try as well. Give them 2-3 OCI to work though not just one. it takes a while to correct the problem.
I never recommend oil additives but Scotty Kilmer recommends AT-205 reseal https://www.youtube.com/watch?v=ZngmqiVezAY&t=180s