Nobody was saying this prior to the Foundation TV series coming out. It seems like marketing wanted to drum up some controversy for their series because the allegations would have required evidence from 40 years prior. Maybe it happened, maybe it didn’t, but definitively saying so either way makes it seem like you have an agenda.
Lol, Asimov's reputation for being, shall we say, physically inappropriate with women at SF conventions goes back, well, for literally as long as there have been conventions.
It's written into the story line of some stories like the mystery solving ones.
But in the story lines, the affections seem very mutual. So I'm not sure it's fair to call him a "harasser". Dirty? Perhaps. Old man? Yes, that's chronological and it can't be denied.