If mouse gestures or keystrokes are not registered on your Mac, try the following steps:
Reset the Remote Management Service
Follow these instructions to reset the Remote Management Service. Make sure that both the Watch and Control options are enabled.
Multiple displays on the remote Mac
If multiple displays are connected to the remote Mac, a known macOS error may prevent the cursor from moving. For more information and workarounds, see this article.
Check your settings
Interaction mode
Make sure that Control mode is selected in your connection settings, as Observation mode does not allow mouse or keyboard input. Screens remembers your last used mode. So if you ended your last session in observation mode, this will be used by default for your next session. You can change this setting via the action button in the toolbar (on the far right of the toolbar) and select Interaction mode.
Also make sure that Start in watch mode is not enabled in your connection settings.
For more information on interaction modes, see this article.
Cursor control mode
For iPad or iPhone users, select the appropriate cursor control mode. If you want to control your Remote Mac like a trackpad, but have set Screens to touch mode, you should switch to Trackpad mode. Further information can be found in the Article on cursor control modes.
Installed software on Remote Mac
Certain software, such as mouse jigglers or applications that change or interact with the keyboard, can interfere with mouse and keyboard control. Try disabling such software and then try to connect again. If you are able to connect successfully after disabling the software, this indicates that the installed software is not compatible with screen sharing.
Restart your device or computer
Try restarting both the device or Mac you are connecting from and the Mac you are connecting to.