I got the s24u and because in the past I returned 2 s23u because of screen delamination, straight from the box I checked the bottom of the phone to see if there is any delamination. There is to both bottom corners slight creases, whats Samsungs excuse now as the screen isn't curved anymore.
I put side by side my s23u and s24u ,adaptive brightness off,extra brightness on and my s23u is much brighter, also the white looks "whiter".
With adaptive brightness on amd the s24u is way dimmer than s23u.
The colours are a touch dull but not by much ,however, the s24u has a big contrast than s23u,especially outdoors