DC31 - many, many thanks for your simple/straightforward instructions to get darkice/icecast2 running on the RPi4. Worked like a charm. Though I have a couple notes which might be significant for others.
While installing icecast2, there are screens to configure icecast2 (setting passwords and such). I seem to recall a notation that icecast2 won't startup unless this initial configuration is done. I ran through the configuration during installation, and changed the default passwords from hackme. The password then also needed to be updated in the /etc/darkice.cfg file, before darkice would start up appropriately.
I'm using a Sabrent USB (Type A) External Stereo Sound Adapter ($9 online), plugged into RPi4. As mentioned in your instructions, quite sure it needs to be plugged in/discovered, for darkice to work. 'aplay -l' or 'lsusb' will show the device, when connected.
I use it to stream whatever audio is playing on my satellite receiver at home, so that I can listen to various news channels, while on the road.
Johngo