so we need to migrate on Intune Standalone
Why? There is no technical reason to do this, and we (Microsoft) do not recommend this (we don't recommend not doing this either as there may be valid reasons customers want to do so).
The documentation and link you've provided are not about Windows management or co-management, instead they are specific to mobile device (aka iOS and Android) management. Thus, they have nothing to do with getting rid of co-management.
Also, co-management has nothing to do with Exchange so any discussion of Exchange here is out of place and completely unrelated to whether or not co-management is used.