unicorn
I haven't used OpenBSD in long time but You probably can add the command "sndioctl output.level=1" to your OpenBSD system's startup script so it runs every time the system boots up. The startup script on OpenBSD is typically located in "/etc/rc.local".
Open the file using a text editor with root privileges:
doas vi /etc/rc.local
Add the following line to the end of the file:
sndioctl output.level=1
next time you boot your OpenBSD system, the sound volume will be set to 1.