There seems to be some kind of oversight when it comes to how the ranks work in Immortal+.
Right now, on a Tracker.gg profile, Immortal 98RR is showing up as Immortal 1, when in fact it is Immortal 2. The correct ranks are as follows:
Immortal 1: 0 - 89RR
Immortal 2: 90 - 199RR
Immortal 3: 200 - 299RR
Radiant : 300RR+ AND in the top 500 in that region.
Yes going from Immortal 1 to Immortal 2 only requres 90RR instead of 100RR for some reason.
Proof in game: