Technically those options are trivial with a non-defective system like approval voting, but assuming you're stuck with first-past-the-post, that's pretty much correct.
Not quite, even with normal approval voting there's no way to distinguish between voters who want to say "all these options are undesirable and everything is broken" and those who want to say "life is good, I'm cool with whoever" and those whose votes get lost or obstructed. The reason why the notion of a "protest vote" is so pointless under our current system is specifically due to the indistinguishability of the first from the latter ("people didn't stay home because they didn't like the candidates, they stayed home because they're so content!"). Additionally without mandatory voting it's difficult to determine where and how voter disenfranchisement is happening, but at the same time it would be unethical to force someone to cast a vote without giving them the option to voice discontent with the options.
What definition of "approval voting" are you using? I'm talking about a ballot where each candidate is marked "approve" or "reject". With that system, "all these options are undesirable and everything is broken" is reject-all, while "life is good, I'm cool with whoever" is approve-all (and lost or obstructed is obviously no ballot at all; there's not much you can do about that).
