The 19's are lighter, more aerodynamic and they have low rolling resistance tires compared to the heavier, less aero, performance tire equipped (and very hot looking) 20's.
Check out this thread, it's probably a better place to have this debate:
In the video (link below) at about 40 minutes there is a discussion of the range (efficiency) of 19 versus 20 inch wheel. The 20” uses performance tires which are about 15% higher than the 19” for rolling resistance coefficient. For the Ioniq 5 19” wheel they developed a long range type of...
www.ioniqforum.com
Let me know if you're interested.