Help with electret mic
Measure R2 to check that it is 100 kohm.

that was the problem, My resistor had a slightly orangish color which
I mistook for yellow.

and from another comment...

Really thankful, Just wanna ask one more question. I know that it is
common-emitter amplification model which has positive current and
voltage gains. Question is, what does the mic output actually give to
the arduino (the signal), is it voltage or current?

The voltage gain is negative because the circuit is inverting the AC input signal.
The amplifier amplifies voltage AND current but, what is given to the arduino, is a voltage signal mainly.