@Christoph-Hart The creator app won't build for me, I think it's the same kind of issue we had with earlier versions of HISE, lots of errors like:
../../Source/Exporter.cpp:20:20: error: ‘CodeGenerator’ is not a member of ‘hise::multipage’; did you mean ‘hise::simple_css::CodeGenerator’?
20 | multipage::CodeGenerator cg(rootDir, projectName, exportObj);
Your test snippet opens with a blank window also.
However, I noticed that with a debug build the multipage dialogs do display properly.
So I tried the release build with different optimisation settings. (Link time optimisation was enabled for all tests).
-O0 - Dialogs show
-O1 - Dialogs show
-O2 - No dialogs
-O3 - No dialogs