How to return default behavior for combination alt+f4?

Question

ubuntu

Good afternoon.
I am working under xubuntu.
I don’t remember exactly how it happened, either I screwed up, or an update, but I had a problem.
Previously, when pressing alt+f4, a window appeared that offered a choice of three options:
1. End the current session
2. Reboot
3. Shutdown
Now pressing alt+f4 ends the session.
Also, now I can't close windows with this keyboard shortcut.
In the settings editor for alt+f4 is close_window_key.
Further I do not know where to dig.
Thanks in advance.

Answer 1

put a virtual machine to see what is written instead of close_window_key.
despite the stability in most such glitches happen