Virtual screens are "unable to connect" in macOS Sonoma Beta on headless Macs (with no physical display connected)

[dngronglong]

An error occurred during connecting the virtual screen.
OS: Mac OS 14 Beta 3

Device: Mac mini Pro

CHip: m2 Pro

[waydabber]

I am not sure what could be the issue, it seems to work fine here with Beta 3. Can you try recreating the virtual screen? Which app version are you using?

[dngronglong]

yeah, I have already re try create virtual screen, but still got this issue, I use app version is 2.0.2b currently

[waydabber]

Well, I am not sure what the problem is. Are you trying to create a basic 16:9 virtual screen or do you use any special method (there might be bugs in v2.0.2 still)? Did you try restarting your Mac just to be on the safe side? I am still on M1 Pro so there is a slim chance that somehow this is broken on beta3 with M2 Pro but it would not make much sense to be honest.

If you write down stop by step what you do I can try recreating it. Also, you can try resetting the app first (Settings/Advanced/Reset App Settings...).

[dngronglong]

yeah, I reset the App Settings, and restart the APP, then click Create new virtual screen option, choose the 16:9 option (the first option) . I got a notice Virtual 16:9 was created ,after I click the Connect ,I got the Unable to connect virtual screen

[mcnahum]

exactly the same issue here.
I'm connecting to a headless device (cable on HDMI port is disconnect) with remote and it was working fine with ventura

(same issue with the last 1.x and this is why I moved to the last 2.x beta)

[waydabber]

ohh, both of you guys are doing it headlessly? Afaik headless virtual screens did not work with beta2 as well.

[mcnahum]

BetterDisplay is perfect for headless device... can adjust it to the size of the external screen you are using...
I'm using it like that for a long time now

[waydabber]

Indeed. But for whatever reason virtual screens do not seem to work in Sonoma betas in headless mode (it's not new in beta3). It's not clear whether this is a feature or a bug. I did not really investigate this issue since these are such early betas. Generally virtual screens work in headless mode since if you connect the screen while a real display is connected and then disconnect the real display, the virtual screen remains working just fine (so this is a workaround of sorts).

[mcnahum]

I can confirm that plugin a cable is fixing it ... let say it is a temporary workaround

[waydabber]

I'll close this for now with a hope that it will be fixed in later betas or if not then I'll be able to fix it. It will be accessible in the pinned "Known Issues list" as other Known issues:

#992

[waydabber]

Just checked this further, unfortunately we have a macOS kernel error 0x5 when trying to attach a virtual screen when there is no at least one physical display connected during creation. After creation the presence of a physical display does not matter anymore. This issue seems to be affecting DisplayLink as well (saw some random complaints about it but since most users are using it with MacBooks it's not a big issue + Sonoma has no public beta yet). Hopefully Apple will fix this after a while (but they are not obliged to do it since the APIs used are private/reverse engineered ones).

[mcnahum]

Displaylink is used a lot ... let's hope they accept to fix it.
I can see that the external monitor are managed differently with Sonoma .. so they probably changed something

[mcnahum]

Good news, it seams to work fine with 2.0.3 build 20199 and Sonoma Beta 4

[waydabber]

Indeed!