If you use macOS with multiple displays and haven’t updated to 10.13.4 yet, you may want to avoid it depending on your system configuration. While the latest update has been praised for adding formal support for external AMD graphics (Nvidia is not officially supported), it appears to have come with a hell of a caveat — users of DisplayLink technologies and compatible monitors have found their ability to use these solutions sharply curtailed, at best. Other screen-extension tools appear to be affected as well.
DisplayLink is used to allow computers to run displays via USB technology. It’s deployed across a number of different products, and there are software solutions that leverage it in various ways, typically to extend or clone a Mac desktop. And as of macOS 10.13.4, none of those solutions seem to be working — or at least, they’re not working normally. As of this writing, the problem appears to be broader than just DisplayLink; programs like Duet Display, iDisplay, the Plugable Triple Display Docking Station and Air Display all appear to be semi-functional at best. It is not clear if all of these software products rely on DisplayLink, but all of them are having problems in the wake of the 10.13.4 update.
The problem appears to be this: As of 10.13.4, Apple has restricted GPU support to the ports that directly connect to the GPU. The team behind the Plugable Triple Dockstation writes:
If this product is being used with a Mac, we have important news about macOS 10.13.4. This new macOS release only supports displays which are directly provided by a GPU or via AirPlay.
For this dock, this means versions of Apple macOS after 10.13.3 will only support the single 4K HDMI port on the dock which uses DisplayPort Over USB-C technology (which is directly GPU connected). The second and third displays on the dock — the DVI and 2K HDMI ports using DisplayLink technology — will no longer function. Windows and Chromebook computers are not affected, and will continue to work as usual.
To continue to use all dock functions with your Mac, macOS updates must be disabled to remain on 10.13.3.
That rationale has been picked up by other companies, though it’s not clear if Apple has formally confirmed it to anyone. Regardless, it’s a problem that was known to exist in the beta version of 10.13.4 and was not resolved before launch. It is not clear if Apple plans to resolve it at all.
To be clear: This bug does not exist if you connect your laptop or desktop to a GPU-driven port like mini DisplayPort. It also shouldn’t impact any displays driven by Thunderbolt; Thunderbolt is an extension of the PCI Express protocol and any display plugged into a compatible Thunderbolt port should have no problem with external connectivity. But it’s clear from reading various comments in product forums that plenty of people have been blindsided by this change, with no solution from Apple in sight. A handful of products have managed to make a partial improvement by restoring the ability to clone a desktop, but a cloned desktop is not a replacement for an extended workspace.
There’s no word from Apple on whether a fix will be incoming.