I put this series on hold for half a year so I could pile up a bunch of chapters because they usually ended quickly but the season ended in that time, so not many chapters to binge unfortunately. At least it was still enjoyable
I'm just gonna say what I understood. First pretty sure they explain in an earlier chapter how mahoraga can use it's users Cursed Techniques. It is explained this chapter how mahoraga starts adaptation when a technique is used and it is sped up by other uses of said technique, so the assuming the earlier hollow purple was say... 5-10 mins ago in the fight I would say this second purple sped up the process, let mahoraga adapt at least enough to tank it, and then since I don't see mahoraga anymore I'm guessing it sacrificed itself to shield Sukuna. It says that Mahoraga can adapt further to a technique than just nullifying said technique, Mahoraga can adapt further to counter the technique. So since Mahoraga was exposed to infinity for a long period of time it adapted fully then created a counter which then allowed Sukuna to use that powerful cleave which he himself said would usually be impossible without Mahoraga's adaptation and his flexible use of CE. The reason Gojo couldn't use RCT was probably because of the exhaustion and damage of the powerful hollow purple that damaged him as well. Gojo himself admitted that Sukuna wasn't at full power so I think that shows he has a lot more CE to use although definitely not as much as before, and also the whole time Gojo was trying to bait Sukuna's trump card which I don't thing he managed to do in the end meaning Sukuna still has more left in him. Once again Gojo is exhausted and he was confident, maybe too much, which led him to being hit by the cleave which Sukuna said didn't target just him but everything even "existence itself" (might be a bit of an asspull) but I took it as the CT targeted everything and threw Gojo off thinking it wasn't targeting him, in the end killing him. But hey once again that's my opinion and how I understood it, you might have another take on it so feel free to disagree with me.