1. Have a build of Qt 6.2.0 beta 3.
   I could reproduce the issue with the commercial build from the online installer as well as with my own build.
2. Have this build's bin directory in PATH, so Creator will autodetect it.

   export PATH=/home/qtrob/Qt-official/6.2.0/gcc_64/bin:$PATH
   

3. Start Creator with clean settings.

   /tmp/qtcreator-5.0.0o/bin/qtcreator -tcs
   

4. Create a new "Qt Quick Application - Stack" project using the wizard.
   No need to change any defaults.
5. In the Projects view, double-click the file Page1Form.ui.qml.
   Creator will try to open the file in the Quick Designer and crashes.

With Qt 5.15.2 in PATH instead of Qt 6.2, Creator does not crash.