Which major religion forbids yeast intake (and how would you guarantee that) and from which angle does one shine light on a people united in faith but with distinct local food (and yeast) sources to make it "interesting"?

Look at the Seventh-day Adventist Church. Their belief isn’t necessarily yeast but dietary standards in general. Promotion of a vegetarian/vegan diet, and removal of alcohol, coffee, and sugar since the late 1800’s. As far as I know the dietary standards include the promotion of the effects of gut bateria, and the ill effects of eating things like warm bread but not necessarily removal of yeast.

I don't think that seventh day Adventist church is necessarily an example of being we'll adjusted

Just living the longest.

The Catholic Church uses unleavened bread for the Host.

It's symbolic, but somewhat of an interest in this thread.

In that specific case it's related to Judean tradition. Jews also eat that sort of bread for Passover.