There is only one reliable way to do this
How to Set Up Dual Monitors on a Chromebook Laptop!
Got a spare Chromebook lying around your house or workplace? You can put it to good use as a makeshift second monitor for your PC. Standalone monitors are getting more and more expensive, so if you can’t afford one yet, read this guide to learn how to use your Chromebook as a second monitor.
ChromeOS doesn’t have a built-in tool to do this, so you’ll need third-party solutions. We tested a handful of tools (both free and paid), but found only one that worked: Duet Display.
Before we say anything else, we should mention that Duet Display is a paid app (costs $9.99). You just need to buy the Android app on your Chromebook (via the Google Play Store). The Mac and Windows clients are free, as long as you are a paying user.
