When starting the live preview with Qt DS 4.0 (build #626) on Mac, you get:

21:13:27: Starting /Users/jarkov/Applications/QtDesignStudio-4.0.0/qt6_design_studio_reduced_version/bin/qml2puppet-4.0.0 --qml-runtime -I /Users/jarkov/Simple3D/imports -I /Users/jarkov/Simple3D/asset_imports --apptype widget /Users/jarkov/Simple3D/content/Scene.ui.qml -qmljsdebugger=file:/private/var/folders/0k/dhbwd1nn4kg0l26xlbcgm9d80000gq/T/QtDesignStudio-YTxkAr/qtc-socket.XoJLNN,block,services:QmlPreview,DebugTranslation...
QML debugging is enabled. Only use this in a safe environment.
Info: Starting QML Runtime ((null):0, (null))
Debug: QML Debugger: Connecting to socket /private/var/folders/0k/dhbwd1nn4kg0l26xlbcgm9d80000gq/T/QtDesignStudio-YTxkAr/qtc-socket.XoJLNN... ((null):0, (null))
21:13:29: /Users/jarkov/Applications/QtDesignStudio-4.0.0/qt6_design_studio_reduced_version/bin/qml2puppet-4.0.0 crashed.

When you press 'play' on the UI everything works ok,