Input offset voltage for microphone circuit
Can you explain how DC offset at the output is an issue, because I don't think it is DC offset nor that it is an issue.

This is a microphone amplifier, microphones do not work for DC. There are even capacitors (C1 and c3) present to block the DC.

You can do the same at the output: simply connect a capacitor (of 22 uF for example) in series with the output: hey presto, your DC offset is gone.

This circuit uses a single 5 V supply. To do so the inputs of the opamp need a proper "working point" and that is set at 2.5 V by R3 and R4. The consequence of this (the single supply) is that the output will also have a constant 2.5 V DC voltage. But as mentioned, for audio signals this is a non-issue as a simple AC coupling (capacitor in series) eliminates that DC voltage.