I did some more research and did manage to get the MEMS mic working.
Apparently the guide was updated after I did setup my RaspberryPi using the guide which Johnny789 did point out in a comment.
This page (Raspberry Pi Wiring & Test) was last updated on Nov ...
WaveShare WM8960 Audio HAT driver installed OK ("sudo dkms status" responses OK), but device not listed ("aplay -l" shows nothing). How to fix it?
The spec says the HAT is compatible to RpiZ/ZW/2/3B/3B+, but does NOT
mention Rpi4B or buster.
This means buster might NOT be supported.
So the installed driver should work ...
How to identify which microphone on which USB sound card?
Finding the IDs of multiple USB sound cards, with microphones. Also see Ref 1 on How to setup persistent device names on Rpi.
I have two USB sound cards. This is how I identify them:
(1) Plug in one sound card - #1 and (a) $ arecord --list--, (b) $ ...
pigpio uses one of the PWM or PCM peripherals to time the sampling of GPIO (defaults to PCM).
If waves are used then the other peripheral will be used for their timing - so there will be no audio support.
See pigpio sound isn't working.
Unfortunately this is normal.
The original Raspberry Pi Model A and B used a linear voltage regulator to step down from 5V to all the lower voltages it requires for its operation.
Its advantage is that it has a pretty smooth and steady output voltage. But the down side is that the excess voltage is literally being burned. (e.g. a 3.3V linear voltage ...