Op amp voltage regulator using N-Mosfet
Here's a rule that's true for most op-amp circuits with negative feedback:

An op-amp will attempt to make both its inputs the same voltage through the negative feedback path.

Here, the feedback path goes from the output, through the gate-source capacitor of the MOSFET, through the \$10 \mu F\$ capacitor, and back to the inverting input. No DC current can flow through the capacitor, so there is no stable DC operating point for this circuit.

Put as a rhetorical question: what's the voltage at the inverting input? Without considering leakage currents and random noise, there is no answer.