If the client system is running macOS Mojave (10.14), you must grant Horizon Client access to the system's accessibility features for optimal performance of the keyboard and mouse inside remote desktops and published applications.

When you first start Horizon Client on a macOS Mojave (10.14) client system, Horizon Client prompts you to grant access to the system's accessibility features. If you do not grant access at that time, you can grant access later by going to System Preferences, selecting Security & Privacy, clicking the Privacy tab, and selecting Accessibility.