[janejeon]

I think for mathematics a good suspect is probably the Riemann hypothesis, which many other results rely on. We don't know that it's "undecidable", but from what I've read it's probably true and (even more interestingly), we can derive meaningful results from it being "probably"/"mostly" true (e.g. "for 99>% of cases it is true"), even without knowing that it is 100% decideably true.

Super fun stuff, though I'm not going to pretend I understand all of this (I mostly just gleam this stuff from what mathematicians say on Numberphile channel).