I wonder why in MATE Terminal : File : Open terminal is mentioned CTRL + ALT + N as a shortcut to open the new terminal. This shortcut works just when at least one terminal is opened. If not it opens new Firefox. I have to google that CTRL + ALT + T opens a new terminal also when there are zero terminals open. Why there is not the second shortcut in the MATE Terminal menu?
I guess this is normal since the mate terminal is not all the time your preferred terminal emulator.
Ctrl+Alt+T opens the one you have selected here :
Ctrl + Alt +N stands for New Window (N) and is internal Mate terminal shortcut.
If you want, you can do some extra custom shortcut inside Keyboard Shortcut config :
