Since JUCE 6.0.8, Arturia VST3 plugin UIs are not rendered anymore on Windows.
I assume the problem is related to what I reported here: JUCE 6.0.8 breaks right-click in some hosted VST3 plugins
The mentioned commit 455e08 restructures the plugin UI parent window hierarchy. A new
HWNDComponentWithParent class was introduced which does a similar job as the
AutoResizingNSViewComponent for OSX.
From a first glance I don’t think it is a good idea to pass parent pointers to a plugin and afterwards change the parent hierarchy with a timer after the plugin UI has attached. This has already lead to the problem that Softube plugins as well as the KORG Gadget plugin collection cannot be loaded on OSX (see GitHub Korg Gadgets VST plugin UI vanishes on OSX · Issue #614 · juce-framework/JUCE · GitHub). We basically now have the same problem on Windows alhough it affects other plugins.
In all cases it affects plugins from well-known companies and therefore JUCE not supporting to correctly host these plugins is a major problem for us and our customers.
For reference, this is what I see when loading the Mini V3 plugin UI in the AudioPluginDemoHost: