In What differences should I look out for between male vs female speech?, a lot of answers explicitly mention that ending question sentences with の is feminine.
However, this makes very little sense to me, as my understanding is that の is pretty much the go-to particle for forming questions with non-polite speech.
In general, か sounds pretty marginal to me with non-polite speech:
Sometimes, のか works:
(I think のか only fails when you have a 'question word' like 何, どこ, だれ, etc.; it seems to make it sound rhetorical, e.g., 「彼女は何をしてるのか、僕は分からない。」)
And of course の always works:
And as far as I can tell, simply using intonation (or a question mark to represent it) works all the time:
First off, my judgements here might be wrong since they are just my own.
But, if they are correct, my question is: if ending your sentence with の really is feminine, what is the alternative to (5) in usual male non-polite speech? Is (7) the only option?