I've checked DisplayLink web site and I've found this message:
Important Information about macOS 10.13.4 updateAnd I've also found that another USB display adapter like duet display also
http://www.displaylink.com/downloads/macos
We have become aware that installing macOS release Version 10.13.4 will cause DisplayLink connected displays to go blank after the OS upgrade, with the current DisplayLink driver [4.1] installed. Functionality such as Ethernet and audio, where implemented, is unaffected. We have alerted Apple to this issue and are working hard to find a resolution. These features continue to work as expected in 10.13.3.
In the meantime, we have a new driver [4.3] that will enable clone mode, but not mirror or extended mode displays in 10.13.4. If you require mirror or extended mode displays, we recommend that you stay on macOS 10.13.3 or earlier at this time.
does no work.
*We recommend staying on macOS 10.13.3*How bad situation...
https://help.duetdisplay.com/faq/305404-macos-10-13-4-support
Installing macOS release Version 10.13.4 will cause Duet Display stop functioning after the OS upgrade. We have alerted Apple to this issue and are working hard to find a resolution. These features continue to work as expected in 10.13.3.
We would strongly recommend contacting Apple though their bug reporting (https://developer.apple.com/bug-reporting/). It will help have the bug prioritized if Apple is aware how many people are affected by this issue.
We are actively looking into workarounds so that duet is not affected by the macOS bug, and will keep you informed. Please e-mail us if you have any questions. Thank you for using duet.
