After a Linux Mint distribution upgrade you might notice a change in the "Terminal" app: The menu bar disappeared.
Note: This can also be seen on a newly installed Linux Mint, without an upgrade of a previous installation.
Although the application itself is GNOME Terminal in both Linux Mint releases, the default preferences seem to have changed.
New tabs and windows can now be opened with a [right-click] inside the terminal. But if you prefer the legacy method using the menu bar, you can change the preferences back to the previous default.
To do that, [right-click] inside the Terminal window and click on "Preferences". This will open a new window showing the Preferences of the Terminal app.
Inside the "General" section, the first option is whether or not to show the menu bar. You will notice that this is now disabled by default.

Toggle this option and close the Preferences window.
After you start a new Terminal window, the menu bar should now appear again.