rtl8723bs_nic.bin is missing from alpine-standard-3.19.0-x86_64.iso 's modloop.
It has meant that my computer's wifi wouldn't work on boot. I had to add the firmware file to the modloop squashfs image myself.
I don't know how this happened. The firmware file is in the linux-firmware-rtlwifi package. (I would have installed linux-firmware-rtlwifi, but the /lib/firmware directory was read-only, so the apk add command failed.)