My understanding is fermented foods have good microbes in them. They are, essentially, alive.
If you pasteurize them, it kills off those communities. The heat won’t distinguish between good and bad microbes so it’s all dead after fermentation.
We pasteurize milk to kill the bad microbes (feacal colliforms, food poisoning, etc.) for mass production. It works well, …very well. It’s needed at that scale, period. But if you are looking for the living microbes, it can’t be pasteurized.
Fermented foods have good microbes in them while they are fermenting up until something kills them - they are still very much fermented though regardless of whether the microbes are alive or not. The fundamental alteration has already happened.
Now, if you're looking to eat them specifically for the microbes, and not for the flavour, then you'd have to look for something that has not had the microbes killed off, for sure.