This would be more pertinent if you reported their rationales. (Or if someone else would care to do so.)
The verse doesn’t explicitly teach universal salvation of all sinners from sin–or any kind of salvation at all, if it comes to that!
But it does indicate the scope of Christ’s intention and action, and that’s an important component–one shared by Arminians but denied by Calvinists. A systematic exegetical soteriology, like any other systematic exegetic theology, adds up and factors in this kind of testimony for a total position.
Any trinitarian Christian (as you profess elsewhere to be) ought to be familiar with that practice; because the total doctrinal set of orthodox trinitarianism isn’t spelled out explicitly anywhere in the Bible. We put it together from a bunch of scriptural data, each of which testifies to part of it.
To say that John 12:32 does not teach universalism, therefore, is trivially true, but only in the sense that John 12:28 (a few verses prior) “doesn’t teach trinitarianism” either. They both nevertheless witness to important components of each belief: the total scope of Christ’s intention to save in one case; and a distinction of the persons of the Father and the Son in the other case.
Similarly, to say that John 12:32 does not teach universalism, is only trivially true in the same sense that John 12:32 does not explicitly teach salvation of anyone from anything at all: we know salvation is intended there thanks to a logical relation with other related testimony, not because it explicitly says so (which it does not).