Hello,
When Google released the latest version of Chrome OS, v.85, there was an issue making Arduino Chrome App unable to detect some boards.
We have since then updated Chrome App to temporarily solve this issue, while waiting for Google to fix the OS version, or release the next version.
If you update your Arduino Chrome App to the latest version 1.0.15.12, your Chromebook should be able to detect your boards again.
If this doesn't resolve it, please contact us here:
https://www.arduino.cc/en/contact-us and specify your issue in detail.
Best Regards,
Therese