The only other thing I can think of to try with ALSA is to enable the Auto-Mute
amixer --card=sofhdadsp sset 'Auto-Mute Mode' Enabled
If that does not work, I would suspect that pipewire-pulse / wireplumber is muting the Speaker in ALSA during boot
PipeWire - Auto-switching is not working - ArchWiki
delete WirePlumber’s local state and restart the daemon to see if that helps:
rm -r ~/.local/state/wireplumber/
I basically don’t understand why these audio servers like pulseaudio and pipewire always have to be pre-installed and cause problems at irregular intervals for non-users who are happy with ALSA alone. I don’t think you can simply uninstall them either.
Manjaro i3 includes ALSA only and additional audio servers (JACK, PulseAudio, PipeWire) are optional
pipewire-pulse and wireplumber cannot be uninstalled on Gnome, but the services can be turned off (or permanently masked) to use ALSA only.
Issue on this system is not irregular and there are a few ways to unmute the Speaker control after system is booted. A simple workaround would be to automate the amixer command to run with a time delay after login
Create a launcher in user’s autostart folder: ~/.config/autostart/speaker-unmute.desktop with this content:
[Desktop Entry]
Version=1.0
Type=Application
Name=speaker-unmute
Comment=unmute speaker 5s after login
Exec=/usr/bin/sleep 5 && /usr/bin/amixer -qc sofhdadsp sset 'Speaker' unmute
Icon=
Path=
Terminal=false
StartupNotify=false