Imagine a molecule that can create identical copies of itself from some other molecules floating around; not by any "factory" but just by "lego mechanics". This is more or less what prions do.

At some point a slightly different molecule appears which is better at converting the molecules, or perhaps they can convert other types of molecules for replication: the first evolutionary step. Perhaps some other mutation allows molecules to "harvest" the other molecules to replicate themselves: the first predators.

Over time this becomes more complex; from singular molecules and proteins to lots of molecules and proteins.

I don't know what Von Neumann "showed us", but IMHO it's not hard to imagine life starting from very simple and humble origins given the enormous timeframes involved (IMO the biggest challenge in understanding these sort of things is understanding just how long a million or 10 million years is, insofar we're even able to do that in the first place).