We currently fail to select a useful specialization for the call to extract_t here:

class P[T]:
    x: T

class Q[T]:
    x: T

def extract_t[T](x: P[T] | Q[T]) -> T:
    raise NotImplementedError

reveal_type(extract_t(P[int]()))  # revealed: Unknown

https://play.ty.dev/f21605e1-a6d1-4b08-9f8c-c608fe0cbc22

Note that there is some ambiguity here, because of multiple inheritance. But we should still be able to solve for T. Note that it works fine if the classes are final: https://play.ty.dev/a3821fe3-ace6-402d-b257-b74f1fd74238