Good thing Kaneki isn't a human, he's body is practically a Kagune, and also, freezing here doesn't matter much considering Kaneki can release heat from his Kagune, upwards to 4,000 C which will flash vaporize any ice Doma can throw at him.
I mean, Doma's cold temperatures aren't restricted to working only on humans?

His physiology doesn't mean anything unless being "practically" a Kagune means he's resistant to temperatures below like 200°C or whatever Doma upscales from.
Also, his high heat would be useless if he's instantly frozen right as soon Doma pops the Boddhisatva. Since when does Kaneki passively release 4000°C when starting fights? If it's not an opening move, which it's not, then he loses that encounter instantly.
And I don't want to get petty with the chain scales, but demons should have heat resistance up to like 20000°C for tanking lightning.
Wdym limited to his RC cells? That wasn't the condition for why he was resisting the dragon toxin, it's because his body is practically a Kagune, there was no mention at all of more RC cells = more dragon toxic Resistance and to speculate it as such is a headcanon, even people like Furuta who had comparable RC cells to Kaneki were wearing mask to protect themselves from the Dragon Toxin.
As I said earlier, Kaneki can resist biological deconstruction, and the Dragon Toxin which gives people cancerous Kagune formations. Kaneki's body swelling up and (exploding from heat?) won't matter much due to his immortality and ability to think critically and attack while in a liquid state.
You said "Kaneki can resist cellular destruction via resisting RC suppressants which
causes the RC cells to disintegrate". I'm not making headcanons, I'm just going off of what you yourself said.
And as far as I remember, that is the case. The toxin over-stimulates the body's RC cells, and the massive influx of RC cells causes physical, genetic, and cellular mutations. I never said that more RC cells gives you a higher degree of resistance, and I don't know where you got that from. I'm saying if Kaneki doesn't have a way to protect the rest of his cells, then Muzan's biological manipulation would still work.
Can you show him reacting to Danmaku, not by parrying because he'd need to dodge every single one due their greater ap and low-high regen neg.
he hasn't fought someone with danmaku, but considering he'd view those attacks in slow-motion, i don't think it's gonna be much of an issue. Kokushibo does have danmaku attacks of his own, though. and they're a blitz level above his normal speed.