And a full environmental collapse is not even strictly necessary to end civilization. If the climate perturbation is large enough it will cause a mass migration and an economic disaster, either of which is enough to cause a war.

Can humanity peacefully deal with things like half of China becoming uninhabitable by humans? Dunno but if I had to pit humanity against this or the mirror bacteria I'd choose the latter.

And Nuclear incidents caused by climate/ai extremists are way more likely than those.

Environmental collapse is a convenient, very portable goalpost though.