RetroPie

Bluetooth: protocol not available

sudo apt install pulseaudio-module-bluetooth

Add to /lib/systemd/system/bthelper@.service:

ExecStartPre=/bin/sleep 4

sudo systemctl start sys-subsystem-bluetooth-devices-hci0.device
sudo hciconfig hci0 down
sudo killall pulseaudio
systemctl --user enable --now pulseaudio.service
sudo systemctl restart bluetooth.service