How to enable: Switch back to running GUI from TTY in 18.04

The part you are look for is at the bottom from: Switch to Console in Ubuntu 18.04 - How to Leave GUI?

In Ubuntu 18.04, they have changed things around and you cannot get to tty1, it is always showing the display manager / login screen. If you log in, you then cannot get to tty2 because it becomes the GUI for the first logged in user. The tradition of both GUIs showing on tty7 has ended.

You can get to tty3 by pressing Ctrl+Alt+F3, tty4 by pressing Ctrl+Alt+F4, tty5 by pressing Ctrl+Alt+F5 and tty6 by pressing Ctrl+Alt+F6.

You can then switch between tty3-6 by pressing Alt with the appropriate F-key.

Finally, you can get back to the GUI with Alt+F1 for the login chooser or Alt+F2 for the logged-in user's desktop.

To make a long story short use: Alt+F2

If the function keys don't work you can try these instructions.

In summary you can type:

sudo chvt 2

to switch to TTY2.

There is a lot more you can do with commands to bypass the function keys. Please read the link.

If your GUI is not switching and if it doesn't connect to Internet even though you have then you can do :

dhclient eno1
systemctl start systemd-resolved

After that follow these commands from answer by shubham Gaonkar :

sudo apt-get update
sudo apt-get install ubuntu-desktop
reboot

This solution is working for Ubuntu 20.04+.