Lars is faster than me :)
If someone get a similar problem with RPi4, you should note that there are two variants of the kernel involved.
RPi3 by default boot the -v7+ variant that Lars refers above.
RPi4 use the -v7l+ variant (the difference is the lowercase LIMA)
The name of the modules are the same, but the path to the modules is different.
When I moved mye SD card with Buster from a RPi3 to a RPi4 it automagically chose the right kernel.
Jon, I hope you get some help from all this. You could run `lsmod` and see if the two modules are loaded:
If the modules show up, you could see if there is any relevant info in `dmesg` that can give a clue why sound (and probably GPS) is still not working.