Having this issue. On first launch only one instance of my application is started, expected behavior. On subsequent launches I get two instances of the application with one attached to a newly opened terminal window, not expected and yes, undesirable. macOS Sequoia 15.5 (24F74) Xcode Version 16.4 (16F6) Building a C++ application using SDL3 and OpenCV. I found that adding a sleep before window initialization "fixed" the issue. Will be filing a bug report.

Thanks for the reply! I found that the issue was caused by including these lines: #define NS_PRIVATE_IMPLEMENTATION #define MTL_PRIVATE_IMPLEMENTATION #define MTK_PRIVATE_IMPLEMENTATION #define CA_PRIVATE_IMPLEMENTATION in my header. I moved them to an implementation file, .cpp and the issues cleared up.

Thanks for the reply DTS Engineer! Moving the TabView out of the NavigationSplitView element, making it the topmost element in the WindowGroup produces the same results, ie FAULT due to index out of range while switching between the tabs. I still believe there is an issue with the API. That said, now I openly wonder how one may achieve similar results to Xcode's sidebar.