Last I heard about this, there was one guy saying there's problems and the author dismissing that as "they just didn't understand it" without showing much interest in explaining it better...
I recon the general cosensus among mathematicians (as that is what counts) is that the ABC conjecture so far has _not_ been proven. Mochizuki (and his school around him) seem to be the majority of people that believe his proof is correct. As you point out, Scholze has identified a supposed flaw in Mochizuki's argument, but anyone not already at the forefront of IUT/NT/ABC conjecture is probably incapable of telling if this flaw is a true flaw or not. As Mochizuki refuses to elaborate (on this supposed flaw) consensus cannot be reached and thus the ABC conjecture remains open.
If you mistrust authors and can't actually rule out someone trying to cheat, checking a formaized proof beyond a reasonable doubt is still a lot of work and needs a huge amount of domain-specific knowledge. An author trying to cheat would try to make everything chaotic and hard to read, as well as hiding subtle flaws in theorem statements.
Is it still open whether there is a problem?
Last I heard about this, there was one guy saying there's problems and the author dismissing that as "they just didn't understand it" without showing much interest in explaining it better...