This is how to install the Azure Agent on OpnSense.

https://github.com/Azure/WALinuxAgent/?tab=readme-ov-file#installation

Login via SSH or use the Serial console in the Azure Portal. Login as root and get a shell

root@OPNsense:~ # freebsd-version 
14.1-RELEASE-p3

You will need a file editor

pkg install vim 
# or
pkg install nano

Run either of the following commands to install the Azure agent

pkg install sysutils/azure-agent
# or
pkg install azure-agent

Create an /etc/rc.conf.local with the following in it

waagent_enable="YES"

Reboot

root@OPNsense:~ # reboot

You should see "Starting waagent" in the Serial console as the VM boots

Also the Azure portal should report the agent is running too