If ALSA cannot detect hardware audio devices, software audio servers would also be unable to detect audio input and output devices in ALSA. If a user does not have a Bluetooth device to play audio, pulseaudio or pipewire-pulse creates a Dummy Output sink
pactl list sinks
Sink #1
State: IDLE
Name: auto_null
Description: Dummy Output
Driver: module-null-sink.c
Sample Specification: s32le 2ch 48000Hz
Channel Map: front-left,front-right
Owner Module: 9
Mute: no
Volume: front-left: 65536 / 100% / 0.00 dB, front-right: 65536 / 100% / 0.00 dB
balance 0.00
Base Volume: 65536 / 100% / 0.00 dB
Monitor Source: auto_null.monitor
Latency: 65080 usec, configured 75000 usec
Flags: DECIBEL_VOLUME LATENCY SET_FORMATS
Properties:
device.description = "Dummy Output"
device.class = "abstract"
device.icon_name = "audio-card"
Formats:
pcm