Evidently it is no longer possible to ask questions on Stack Overflow without signing up for an account. I have no opinions on this either way, but I do think the following section in the network about page needs to be changed:
The sites are free and open to everyone – you can ask or answer questions without even bothering to register. Better yet, you have access to the full archive of existing questions and answers – again, without needing to give up so much as an email address.
Either that part should be moved to the about page of sites where this is true, or there should be a footnote or something that states Stack Overflow is an exception. I am not sure if there are other places where this needs to be updated as well.
Additionally, the "why register?" page on Stack Overflow reads as following:
Registration is not required to participate on Stack Exchange; you can read, answer, and suggest edits as an anonymous user, much like on Wikipedia. There are some things you won’t be able to do on the site without registering, however, such as vote. Registering is easy, and once logged in, you can gain other key privileges by earning reputation.
This should also be updated to explicitly mention asking questions (a somewhat major feature) as being a thing unregistered users can't do.