Why Is Anybody Convinced There Is A God?

"Subjective" basically refers to location. Namely, saying that x is subjective is saying that x is a mental phenomenon, or in other words, it's occurring in a brain functioning in ways that amount to mentality.

So whether something makes sense or not is subjective, because making sense to someone is a matter of whether they're in particular mental states in relation to it.

Beliefs are also subjective--beliefs are mental phenomena.

In my view, truth is subjective as well, though that hinges on a technical issue re how truth is viewed in analytic philosophy (namely, it hinges on the fact that truth is seen as being a property of propositions, and then it's an upshot of my analysis of what propositions are ontologically, what properties of propositions are ontologically, etc.)

What a lot of people are referring to in their truth talk is something like, "What's the case in the world objectively (mind-independently)."  But we call that a fact in analytic philosophy, and there's a standard, technical reason that there is a significant distinction made between facts and truth(s).