Many Apple users have a complaint that External Display not working on their MacBook Pro/Air. They said that this problem occurred after updating macOS Mojave. Here I am going to tell you the solutions for Mojave dual monitor not working issue.
Fix 1: Change/Replace DisplayPort Adapter
First, change your DisplayPort Adapter and try the new one. Because the problem may be in the DisplayPort Adapter.
Fix 2: Force Restart
Fix 1: Change/Replace DisplayPort Adapter
First, change your DisplayPort Adapter and try the new one. Because the problem may be in the DisplayPort Adapter.
Fix 2: Force Restart