The origins of bread go back to the advent of agriculture. Sedentism and agriculture are related, but some cultures lived for millenia as one but not the other.

The oldest "recipes" known are, basically soup and bread. Soup could be made in leather or organ sacks, or later with the advent of pottery, in a cauldron. Grindstones go back much farther than agriculture. Note that communities living in fertile environments can exist in what amounts to nomadic pastoralism - rotating through the same marshes and pastures on an annual basis, damming creeks, and manipulating the environment to facilitate native grasses and cereals. Is this sedentary? No. Is it agriculture? Kind of.

The earliest known bread is from the natufian culture and before, though we might call it a pancake (12th millennium bc). Salt was not involved to my knowledge, and it is not strictly necessary, though it is reasonable to assume communities with access to saltwater may have used it. It is likely bread is far older though, given the age of known grindstones, ranging from 60k to 30k years old, though there is no proof of bread.

Cereal is ground, and natural yeasts make the bread rise. Ancient bread was "sourdough," using starter from the previous day. The short answer is that bread is pretty easy to make after your process the cereal.

As a final note on leavened bread, there is pop culture debate of "bread vs beer," and what the earliest drivers of agriculture were. It may have actually been malt, which is processed cereal with higher sugar content, but ultimately led to more robust bread and brewing industry in prehistoric societies.