I have been fighting to bring up bluetooth audio using yocto and I was trying few options pulseaudio and pipewire are one’s I was finally getting to work and I was stuck in starting pipewire systemd services in usermode and it would always complain about not being able to connect to bus and then I tried to use root user and media-session wont start since pipewire does not set it up as root user. I accidentally bumped into this post
which saved my day. I replaced dropbear with openssh for ssh daemon and I was able to start the services properly using remote ssh connection and finally play the audio from a rk3388 board to my bluetooth headset.
It seems dropbear does not have full support for PAM and that was the key. We should be careful of chosing base components. Always understand the end usecase thoroughly before making decisions on which components to use to build your embedded linux stack.