I solved the problem. I erased the iPad again. When I went to installed the beta profile, I realized that before I may have installed the wrong profile (iOS instead of iPadOS). In both cases, the device was already in iPadOS beta 3. However, the second time, after I installed the right profile I was offered to download an update. I accepted and after that I was able to enable developer mode.

The problem is not related to archiving. It occurs when the you launch the app in non-debug mode, which happens to be the case for Archive. But other ways to see the crash are, launching the executable from Finder (doesn't have to be the one archived), or uncheck the "Debug Executable" option in your the "Run" profile of your active scheme in Xcode. I found a workaround, which is effective, but seems completely unrelated. This crash does not occur, if at some point before you display the VideoPlayer, an NSTextArea is displayed. But not just any NSTextArea. It must be loaded with an RTFD document. But not just any document, one that contains an image! More details can be found here: swiftui-lab.com/videoplayer-bug

I also found that in the official documentation all mention of macOS has been removed: https://developer.apple.com/documentation/scenekit/sceneview Does this mean SceneView is gone for good? I think this merits at least a comment in the Release Notes, so people can plan accordingly. Anyone from Apple listening? Can you confirm, or deny... or just comment...