Variable frequency means precise that. It will be variable, it will not be maintained at top speed. Power (voltage) is what is gonna be maintained. That way unused voltage from cpu can be transfered to the gpu to make the boost when is needed.
Mark Cerny's PS5 Presentation (35:54)
"...We run at essentially at constant power and let the frequency band "vary" based on the workload"
Mark Cerny's PS5 Presentation (36:47)
"...We look at the activites cpu/gpu are performing and set the frequencies on that basis..."