Can someone explain what is the correction factor for?
It's an attempt to standardize for overall race difficulty, and I think they primarily like to use the kJ/kg metric of the overall stage. I don't know why Finestre gets such a big addition now because they did under 2000m of climbing going into the base, though perhaps the high altitude and gradient also has to do with it. Oh and Finestre, so it must very likely be the gravel. Funnily Sestriere only gets a +7 correction on it.
I can't find where they explain how they standardize it now, but they were pretty open that they do not take into account drafting and wind, which is why they tend to get high numbers on shallower climbs for larger groups, which leads to the entire top 10 doing their seasonal best on the low altitude 6.5% average Montserrat climb in Catalunya for example.
Essentially by correcting for overall fatigue and these other factors they try to rate different climbs in different stages at different fatigue levels. So today would be a 90 rated performance if it was all asphalt I think.
It's a higher rating than any so far this year, and last year Pogacar, Vingegaard and Evenepoel (once) beat that rating
Funnily enough the index is supposed to be from 0-100 but Pogacar broke it last year as Plateau de Beille hit 111 on the index