Zener diode in parallel with both the input terminals and the output terminals
First a correction: they are diodes or schottky diodes, not zener diodes!

The idea is that if the voltage is connected the 'wrong' way, that the diode starts conducting in the forward direction and short-circuits the input. The the fuse blows and the circuit is safe.

Although nice on paper there is always the question: what blows first, the diode or the fuse? For this to work your fuse has to be small and light and the diode has to be heavy and robust. Also this does not work if power comes from U8. (But I thihnk that should not happen anyways. But what is D3 for then?Seems a bit redundant). I also have some doubts about SS12. There will be a voltage drop over the shottky? diode and your NodeMCU does not get the full 5V.