I get an denied/forbidden mouse cursor and cannot control the remote computer

This cursor indicates that AnyDesk or the remote device has not given you the permission to control this part of the user interface or application.

Please also see I cannot use AnyDesk to manage my Security/Anti-Virus Software.

In most cases, installing AnyDesk or launching it as an administrator on the remote endpoint can resolve the issue.

Performance and Enterprise license users can also create a custom client that automatically requests administrator privileges upon startup if AnyDesk is not installed. See also Customize AnyDesk and Administrator Privileges and Elevation (UAC)