My dealer supplied 4 level service schedule only mentions 'service brakes' on service 3 ($379 CAD), which I'm pretty sure is just a visual inspection and possible adjustment/lubrication of the service and parking brakes if the pads and rotors are still good - definitely wouldn't include a brake fluid flush. Any additional parts required like pads or rotors I believe would be extra cost as well.
They do include a side sheet of 'additional services' (which are not part of the KIA service schedule) where they offer an extra cost brake fluid flush at a 'suggested' interval of 3 years/36K kilometers, along with GDI cleaning, alignments, etc.
However, my OM 2018 service schedule calls for brake fluid inspection only, every 2 years or 12K miles/20K kilometers - no set flush/replace intervals out to the 15 year limit of the schedule. If I was tracking the car, that's a different matter - but it's not required by KIA's service schedule (that's the bible to me), and is not something I'll be doing for my non-competition car unless I see contamination or develop a leak.
I'd be interested to hear what the OP's dealers reasoning was, to flush it on a 1 year old (or less) car.