I keep having this more and more often when I am changing between screens I get TSW 6 locking to the screen, not interactable, and I can't use [Alt]+[Tab] to any other or close it. Launching task viewer/task manager isn't much use as soon as I select it on the tray it flips back to TSW 6 which is input locked and will not do anything no matter how long I wait and cannot be closed despite applications are still able to be opened in the background. Why is it doing this and how am I supposed to move it off the screen without unplugging the computer?
I encountered a similar hiccup today. Not quite the same though. In my case, I was doing some Free Roam, looking for photo opportunities along Maintalbahn. Activated the map. While in the map, I hit Alt+Tab to check on the podcast I was listening to in the background. When switching back to TSW, I could still scroll and zoom the map, but nothing else. And I couldn't leave the map either, none of the ingame keyboard commands would work. Only solution was to go Alt+Tab again and close TSW manually, which it did without hassle. The issue hasn't reappeared since.
I keep finding TSW6 will freeze when I alt-tab and it takes several toggles to get it to start updating the screen again. Not a behaviour TSW5 and earlier have.