PulseAudio monitor is not picking up microphone

[sctse999]

I have exactly the same issue described in the link below except that I am using ubuntu 20.04. I use PulseAudio as the backend and choose "Monitor of .... Speaker + Headphones" as source. This same setting worked before but recently it has a problem of not picking up the sound from the microphone. I understand that this maybe an issue of PulseAudio but I appreciate any pointers that I could solve this problem

https://unix.stackexchange.com/questions/695905/cannot-record-microphone-with-simplescreenrecorder?newreg=fd51d3add1444cc9be32bcefd44324dc