With the update to 2019, Infraworks moved from its own cloud groups to utilize the BIM 360 Document Management Service. This change brought the loss of a few things as well as the gain of a few things but one big issue that is occurring is that if a User has been invited to a projects docs service, they lose the ability to save their project locally and are forced to push to the cloud.
An example of the situation could be that a user is invited to another companies host for a project, while their own firm does not have a bim 360 subscription. Now if that user would like to use Model Builder for one of their own projects, they cannot save locally. This should not be the case.