Please tell us more about what you intend this MCU to do.
Most of us volunteers/hobbyists here don't know what an Intense Pulse Light medical device does, or how and why it does what it does.
But we do know about microcontrollers.
For example, if you only wanted the microcontroller to turn a "lamp" on for a certain fixed duration in response to a "trigger" e.g. a button-press, then any of the simplest / cheapest stm32c0 would have plenty of power, as well as being small and cheap.
Where the unit is battery-powered and spends most of its time not shining the light, you might get better battery-life with something from the stml0 family.
However if the "lamp" needs more careful control, perhaps ensuring a fixed known intensity (measured by a sensor then an ADC) by e.g. pwm-modulating the drive to the lamp, you need to look at a slightly more advanced microcontroller from the same family.
On the other hand, if this medical device had a "user-interface", so a screen and more than a couple of buttons or a full-blown touchscreen, then you need a much more powerful stm32 with many more pins.
But we need to come back to what is "best".
One of the most expensive things in these products is your time and effort to get <whatever> to do what you want. So any stm32 demo board that you can obtain and be pretty confident that it has more-than-enough power to do your task might work out as the best one. And once you have it working with flying-leads from the demo board, take the minimum-effort route to turn it into your own design i.e. copy those bits of the demo-board's schematic that you use for your own product board.
