Following up on my previous comment, here's the last two as dataclasses:

@dataclass(frozen=True)
class Just:
    value: Any
    def __or__(self, f):
        return Just(f(self.value))

and

@dataclass(frozen=True)
class Nothing:
    value = None
    def __or__(self):
        return self

No boring bits!

(And yes, I did try it out, and a dataclass with no fields at all is completely OK, which is good, but not totally surprising because it is the right choice.)