Connecting to a Mac
If Screens is connected but no image is displayed, try resetting the Remote Management/Screen Sharing service. This may be necessary if an issue arose during the upgrade process, after using Migration Assistant, or following certain macOS operations.
This article includes steps to perform this operation.
Other Options
If resetting the Remote Management service doesn't fix the issue, try setting either or both Image Compression or Adaptive Quality to Never in the app settings under Controls.
Connecting to a PC
If you’re connecting to a headless PC or a laptop with the lid closed, the display may appear blank because the operating system might pause the display driver. For more information and potential workarounds, please refer to this article.