Without some concrete evidence that Kia has changed the mapping, tuning, or random parts sometime between the 2018 and 2020 models, we’re all just spewing conjecture. There are multiple variables that can effect 0-60 times: atmospheric pressures, temperatures, elevation, heat soak, fuel, weight (how much extra crap is in the car, how heavy is the driver), tires, etc. Forming an opinion based off of constantly changing variables and then presenting them as fact is lazy and makes no sense.
Could a 2020 be faster than a 2018? Sure, see the variables above. Could a 2018 be faster than a 2020? Sure, again see the variables. Is either one ACTUALLY faster than the other from the factory? Without concrete evidence of tweaks from Kia, no.