No, this question should not be on-topic, even though it deals with the physical problem of vision.
Yes, the scope of Lifehacks is about physical problems, but it's also about lifehacks, not software configuration. The question specifically is asking for iPad settings to reduce eye strain... it is not looking for general eye-strain reduction advice. Just because eye strain is a physical problem doesn't mean that the specifically-worded question here that involves eye strain is on-topic.
It's a question asking about how to configure a tool to do the job it's meant to do. It's not a question asking for an unconventional solution to a physical problem.... in fact, the question specifically has narrowed the scope of answers to just the conventional... adjusting the iPad settings. That is not what this site is about.
There probably is an on-topic version of this question that expands the scope to cover more than just iPad settings. However, I don't believe it's in our best interest to just ignore the restrictions of a question and assume the more general scope, as Mooseman did in his answer to the question. There's the whole idea of XY Problem where you want to solve the problem they're really having, and not the one they're asking about, but I don't think that's what we're dealing with here. Changing the iPad settings might be a perfectly acceptable way of reducing eye strain. Changing the scope of the question for them wouldn't be solving the XY problem... it'd simply be changing the question so that it fits better what we want on our site. That seems inappropriate.