Not sure exactly what changes but I think it is the damper stiffness. You get more high frequency 'patter' in
cupra mode compared to comfort as it picks up the smaller road imperfections. Apart from that it doesn't feel that much different until you hit bumps or sunken drain covers. If you do this in
Cupra mode it feels like you broke the wheel and indeed you spine due to the stiffer damping and I guess reduction in damper travel