Before discovering Cantabile, I used another “popular” VST host program that allowed the user to minimize VST plugin Windows and return focus to the host program without actually closing the plugin. I found this very convenient when bouncing back and forth between a plugin and the host to adjust settings.
In Cantabile, it seems that the plugin window cannot be minimized. There is probably a good technical reason why it was implemented this way and this topic may have been discussed previously. I can tell you that my workflow was easier when I could toggle between the plugin and the host and leave the plugin window(s) running in the background, particularly with large VSTs like B-3X that take several seconds to load. I thought I would offer this as a feature request, if it hasn’t already been brought up.