And how could I get back to the view I had before in this window?
What you’ve got open in the screenshot is a Quick Reference window. You can hide the bookmark sidebar on the left by clicking the bookmark icon in the footer, just to the left of the word count, but Quick Reference windows can’t show the binder. That’s part of the main project window only. If that’s minimised or hidden, you should be able to recall it to the front via the Windows task bar or using the Alt+Tab shortcut to switch between running tasks.
In the main project window, you can hide or show the binder by toggling
View ▸ Binder. For more on Quick Reference windows, you can check out section 12.5 of the user manual.
OK, thank you very much!