µA/MHz shows how much current will be consumed scaled per clock frequency.
263 µA/MHz at 400MHz, means that 0.263*400 = 105.2mA is consumed.
This is probably only for the core with oscillators (PLL) included. If you enable peripherals, they will also add a certain amount of µA/MHz to that figure. For absolute worst case, you would need to enable all peripherals at once, at the highest frequency, and "exercise" them such that they consume their max power.
Considering the large amount of peripherals that the STM32H4 has, I believe it that the chip could consume well over 125 or 150mA in a typical application. Ethernet, USB, external memory controllers, high-speed GPIOs all consume a fair amount of power.
165mA is not "typical", however it's always nice to design the hardware for corner cases like this, e.g. everything will stay working with maximum power consumption, temperature, etc.