There are a few reasons why your display may not be working after an update:
1. Display settings: Your computer may not recognize multiple monitors if the display settings are not configured correctly.
2. Faulty cables or ports: Hardware issues, such as faulty cables or ports, can also cause detection issues.
3. Software or driver problems: The problem may be due to software or display driver issues. Ensure you have the latest drivers installed and consider updating or reinstalling them.
4. Physical connection: Check that the second monitor is properly connected and turned on. Restarting the computer can also help resolve any connection issues.
Consider checking these factors to determine the cause of your display problem after an update.