You can manage virtual external displays for physical devices if you want to test the external display experience. It is not supported for simulators through Device Hub. If this is something you relied on, please file feedback at bugreport.apple.com. If you do, please include an example of an application for which this worked in Simulator with iOS 26 because my understanding is that this feature has been completely unusable in iOS simulators for a few years. I'm wondering if there is something I'm missing, thanks!

Don't use sudo. Using sudo operates on root's sims, not yours ;)

No. Please do not delete all of Xcode and redownload it and resintall it. That's serious overkill for what is probably a very simple problem. Per the OP, the issue was that the system resources installer got interrupted and left the system if a partially updated state... so just finish that process. I suggest you run: xcrun devicectl manage ddis update That will probably address the issue. If not, the following will reinstallt he the system resources package (including the DDIs): sudo installer -target / -pkg $(xcode-select -p)/../Resources/Packages/XcodeSystemResources_Full.pkg