Is there anything that cannot be criticized, or cannot be treated with scepticism ...

There are certainly circumstances where expressing doubt, criticism, or skepticism is not indicated. But that’s not the same as saying it’s not possible.

The problem with the original post here is that there aren’t really any non-obvious answers. So it strikes a lot of forumgoers as a pointless question to bring up.

I have heard that many things cannot be questioned, on the moon.

This has been famously disputed by the alternative theory of “Earth sucks”

No, that too.