None of the above. Shaker style is from the craftsman era and before. A flat panel door would be appropriate for MCM.

I had not thought Shaker doors were mid-century modern. Instead, think flat front doors, often in wood. I bought a MCM from the original owners and all the doors were slabs, by then painted white. Since the bedroom area looked traditional, I replaced all the doors with two-panel (raised panel) doors. And there aren't any doors, except the front and back doors, in the part of the house that still looks MCM. So I think it depends more on what your interior decor is - if it is very MCM, then more modern doors. If it leans in other directions, choose the doors accordingly.

Agree with @cpartist Flat slab doors should be what you pick.

Unless your home is a true MCM "museum" that has never been touched, then sticking to a strict style choice might not be as important. I would probably keep it simple with the single panel.

I used a 3 panel door in my Spanish inspired house, but added a detail inside the square edges to soften the look.

I agree with cpartist too. Flat panel door if your house is mid century, no shaker doors. They are not appropriate.