To me it seems like another one of the seeming invincibility and specific conditions combo like BM and Kata and Kaido and King. There is a technique for the counter like against Kata and Kaido for the slow regen effect and there is a specific condition for the counter like BM and King for the Imu regen (the problems as they seemed at that point in time). I think the real body in the abyss needs to be targeted.
If we look at the situation I think it is easier to describe the Zoro confirmation as him learning a skill like he did against Mr.1 (haki) and recently against King (ACoC). But like Zoro said he needed to be able to use the haki skill whenever required even after beating Mr.1 but he didn't know what it really was and could not use it against future Logia opponents like Enel and the sword rusting guy. Here Zoro has ACoC the answer to the HKs/Gorosei but now has knowledge about the skill and can counter the HKs/Gorosei (Logia).
The theory that made the most sense to me so far is that CoC has to
linger on subjects outside of the user.
To mitigate the regen of HK's, you need to have your CoC linger in their body after your attack. The longer it does, the longer their regen is supressed and you can kill them.
To create a black blade, your CoC needs to linger in the blade permanently. And it's why it can't just be forged out of the blue. You need time and lots of battles where you pump that CoC.
Shanks did it to Greenbull. He caused his DF to regress and prevented its use. And, terrifyingly, from a far distance.
And I bet that's what Zoro did to Monet. We know that Zoro has been used to preview haki abilities in hindsight: with Armament/Ryou and Observation against Daz, Asura (COC susano? lol) against Kaku, so it wouldn't be surprising if Zoro pulled a mini version of what Shanks did to GB. Tashigi mentioned she couldn't detect any haki used against Monet, but she, just like Kaku and Zoro/Sanji recently in Elbaf, probably can't truly discern CoC. It takes a certain fluency and experience to detect it like Gaban/Luffy did for Zoro.
So Zoro basically sliced Monet and imbued his CoC into her without realizing or understanding it, and she failed to put herself together with her fruit. It was just "fear" at the time, but in retrospect it would make a lot of sense.
I think that's what M3 have to figure out this arc.