Is truth singular or not? In physics, there's general relativity and quantum mechanics, and both are true, but these are theories. Within reality itself can two contradictory systems coexist, or is there one truth and one truth only and anything that opposes this truth cannot exist?
Long story short: no, following any of the dictionaries definitions, there are multiple truths, which depend on multiple facts. To get a philosophical systematization of such concepts, better googling for theories of truth.
QM and relativity are currently not coherent . This essentially means that predictions made from a QM perspective are different from predictions made with relativity. Following the principle of explosion, if there's a falsehood in a coherent logical set of propositions, the whole set is false. So, both theories would be false. But, believe it or not...
...this is expected! Science has not the goal of finding final truths, but empirical truths, that is, truths that are coherent with our experience (we don't have other interface with the world that our not-so-trustworthy senses). In fact, we already know that our experience has multiple flaws . So, it is expected that extrapolating formal consequences to extremes will lead to falsehoods.
Here, enters philosophy. The goal of philosophy, as the mother of all sciences, is finding final truths (or truth). But the problems which philosophy address are huge. Worst even, we also expect (currently) not knowing the truth. Ever. (e.g. we don't have access to the noumena ).
That means that your question, in strict terms, would be impossible to answer.
According to the slingshot argument, although there are arbitrarily many true sentences (or propositions), these all have One True Fact (or a singular Truth Value) for their reference. Sometimes we might speak of a "big conjunctive contingent fact" (see here) as comprising some concrete world.
The disquotational scheme says that
"Sp," is true if and only if Sp
If that's "all there is" to a sentence (or proposition) being true, then in that way there is only "one" truth, i.e. there is only one scheme that fixes the use of the word/concept "truth."
Truth being singular is an abstraction already introduced in ancient Greece. It was ssid there could only exist one god instead of the many in polytheism. We still bare the consequences. This god couldn't (wasn't allowed to) be imagined. This is the attitude of many modern day scientists and theologicians.
Truth is dependent on people though. If I belive in many gods then they are there. If I belive in curved 4d spacetime then it's there. If I belive only in mathematical structures then they are there. I maybe don't know the true Nature of the gods or the mathematical structures or of rishons (sub quark particles) but I have for sure a relation with them. Other people can never say that I lie when clining to a truth. Of course I can lie if they ask me what truth I cling to.