TENANT ADMIN Screen sharing will be declined if only the IM modality is enabled in tenant settings.
This page is describing standard SfB functionality from an Agent's perspective. No further configuration is required to use Desktop presentation.
An Agent may start presenting his screen or program for the customer by starting sharing session in SfB client, and customer will receive video stream on his side regardless of active conversation type: IM/Audio/Video.
Screen sharing can be initiated and stopped only by the Agent.