Explicit background app transparency is a feature introduced with macOS 27 Golden Gate. The indicator dot appearing on the Dock for applications still running in background changes its color. Additionally, when you hover over or right-click that app, "Running in Background" is shown.
Current Steinberg programs use the "Steinberg License Engine" and often the "SteinbergMediaBayServer" background processes that continue to run for ten to fifteen seconds after the main program (such as Cubase or Nuendo) has been closed.
During that time, the app will remain in the Dock as "running in background" showing the light gray indicator.
In macOS Golden Gate in General -> Login Items & Extensions under Background App Activity, it is now possible to set the background app activity to on or off for each application individually.
We recommend leaving the option to allow apps from Steinberg to run in background switched on.
This is especially important if you work with more than one Steinberg application at the same time.
As every application requires at the the Steinberg Licensing Engine process to be available, quitting one application that is not allowed to run in background would terminate that process for all other applications as well. This can lead to crashes and instabilities.
Even if this means that the closed app will remain visible in the Dock, it does not consume any additional resources anymore.
More on apps running in background can be found in this Apple support article.