HPF cut-off in microphone pre-amplifier
They both do.

The electret microphone with its JFET buffer behaves as a current source, with a very high output impedance. In terms of the AC analysis, this is in parallel with Rbias, since the upper end of Rbias is at AC ground. The Thevenin equivalent of this is a voltage source in series with Rbias.

This means that the current flowing toward the opamp is determined by the Thevenin source voltage divided by the series impedance of Rbias+C2+R2. The cutoff frequency is

$$\frac{1}{2\pi(R_{bias}+R_2)C_2}$$