Hi,
Thanks for posting in Q&A platform.
The second monitor cannot be detected on Windows 10 may caused by several reasons, please refer methods in the following articles to see if the issue can be resolved.
How to fix second monitor not detected on Windows 10
Solved: Windows 10 Not Detecting Second Monitor
Please Note: Since the websites are not hosted by Microsoft, the links may change without notice. Microsoft does not guarantee the accuracy of this information.
Best Regards,
Sunny
----------
If the Answer is helpful, please click "Accept Answer" and upvote it.
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.