Allow SimpleMDM to release devices without having to sign in to Apple Business Manager. This feature is enabled by default when you add an MDM server in ABM/ASM. You can remove this feature by deselecting the option for any new or existing MDM servers you created.

But SimpleMDM has not implemented this feature yet. Would be nice to automate the decommissioning process of the devices.

https://support.apple.com/en-sg/guide/apple-business-manager/axmec4d28461/web