Use older Juce look and feel for the file browser. Not looking too great but better than the current default look and feel...

Source/PluginEditor.h

@@ -487,6 +487,7 @@ private:
 	
 	std::unique_ptr<MyFileBrowserComponent> m_filechooser;
 	WildcardFileFilter m_filefilter;
+	LookAndFeel_V3 m_filebwlookandfeel;
 	JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (PaulstretchpluginAudioProcessorEditor)
 };