Zener Shunt Regulator Question
Do not do this. It's dangerous.

What you're doing is dangerous. Always, always, always have galvanic separation between your high-voltage source and your low-voltage output.

Your bridge rectifier, if it fails, with a high probability fails in a "closed" state, so that you end up connecting your output to grid voltage.

Whoever recommended this as general solution to the problem of generating 5 VDC out of 230 VAC is a dangerous person.

Do not do this. It doesn't regulate well at all, and wastes power.

There's literally hundreds of posts on here that explain why regulating voltage by parallel Zener diodes is a bad idea.

It's not stable. It wastes most of energy. It's, due to the required size of diode and cooling, more expensive than a linear regulator IC.

Whoever recommended the right half of the circuit as 5V regulator for the DC coming out of the bridge rectifier lacks the skill to use modern (as in: since 1977) components.

Do not do this. It's overly complicated and expensive.

Any USB charger is a 5V regulator. Buy one. They are isolated, properly regulated, properly enclosed, come with an actual plug....

You can also buy a proper power supply module. These are typically far more expensive, but can more easily be integrated in devices. Then again, I've actually seen devices where when you open the box, you'll find a plugged power supply inside: Buying a certified, cheap, off-the-shelf power supply is so much cleverer than designing your own circuit.