They don't have the same bi-modal exhaust ( rear mufflers ).
Your 2018 most likely had the Australia only option of bi-modal rear mufflers that look like this ( like I have ).
View attachment 82914
Then in ~2021 Kia factory fitted the below Bi-Modal mufflers ( which you would have ) and they are nowhere as good as the above for sound and flow.
View attachment 82915
There are a number of solutions but the easiest is a cat-back system.
If you want to keep your bi-modal mufflers but bump up the sound a little, replace the mid-section ( before these mufflers ).
Many options available but everyone has different tastes and solutions to suit those tastes.