I'm not that deep into it and as you noticed information on the issue is sparse. My understanding is that it is not possible to get power management working for these cards (see https://nouveau.freedesktop.org/PowerManagement.html). May not seem like a big deal, but as far as I understand this means the cards are stuck in the lowest power setting i.e. perform as well as an iGPU.
And from my understanding this is forced by Nvidia because power management is disabled when loading unsigned firmware.
That is my understanding of the situation. Due to this the devs basically gave up on those cards as it is unfixable.
Hm, I personally prefer that tbh. I hate missing stuff in my old gmx mailbox because it suddenly decided everything is spam. But I get very little of it.