Keyboard shortcut to switch user accounts

In the latest Ubuntu LTR (18.04 - bionic) I've noticed that you can use CTRL+ALT+F2 / CTRL+ALT+F3 for instance to directly switch to the session of connected users. I'm not sure if it works for users without a current session nor if it extends to other TTYs as more users are connected...

There is also CTRL+ALT+F1 to display the login screen with all users listed.

Although those TTY used to be terminals I have to admit this is quite useful now that many people mainly work on a GUI...

You can open the settings for shortcuts: System -> Preferences -> Keyboard Shortcuts and add a custom shortcut to start the gdmflexiserver. After that you can switch with the shortcuts strg+alt+F7 and strg+alt+F8