While working on #3322 I have found two more crashes:

N = NamedTuple('N', [('x', N)])
n: N

crashes with RecursionError and

class N(NamedTuple):
    x: N
class M(NamedTuple):
    x: M

n: N
m: M
lst = [n, m]

crashes with AssertionError in join_instances_via_supertype. I didn't try TypedDict but most probably it will have similar problems.

There is actually a fundamental question here: what should be the join(N, M)? @JukkaL do you have any ideas? One possible option would be to detect recursive joins and just return object for them (maybe also UninhabitedType for recursive meets).