The supply voltage of stm32 is generally 3.3V power supply of peripheral devices, and the reference voltage of ADC power supply core voltage is generally about 1.2-1.8V, but it is not necessary to introduce STM32 itself. In order to simplify peripheral circuit design, it is generally not necessary to introduce additional kernel power supply pins, so that you only input one 3.3V. Other voltages are obtained by internal linear regulation.
This is different from the design of FPGas, which generally require 1.2, 1.8 and 3.3 three-way power supplies, and the low-cost controller stm32 is not designed to be so cumbersome. But as for how many voltage areas there are inside, this data book should explain.