Cannot start GUI applications “Error: cannot open display: :0”

I am getting this error when trying to launch Thunderbird (or any other program, such as evince):

❯ thunderbird
Unable to init server: Unable to create socket: Permission denied
Error: cannot open display: :0

❯ thunderbird -v
Thunderbird 68.10.0

Any ideas?

❯ cat /etc/linuxmint/info
RELEASE=20
CODENAME=ulyana
EDITION="Cinnamon"
DESCRIPTION="Linux Mint 20 Ulyana"
DESKTOP=Gnome
TOOLKIT=GTK
NEW_FEATURES_URL=https://www.linuxmint.com/rel_ulyana_cinnamon_whatsnew.php
RELEASE_NOTES_URL=https://www.linuxmint.com/rel_ulyana_cinnamon.php
USER_GUIDE_URL=https://www.linuxmint.com/documentation.php
GRUB_TITLE=Linux Mint 20 Cinnamon

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Author: Philippe Massicotte

Run GUI Application from web-based terminal emulator ubuntu18.04/Jupyter Notebook

I have installed a fully-functional terminal emulator in an IPython/Jupyter notebook. This is useful for notebook environments that don’t provide shell access. The terminal is used inside the browser. All commands are executed correctly. But, there is a problem with opening a GUI application from the web-based terminal. Web-based terminal screen

For instance, executing xclock inside the terminal does not open the application window. Is there any feasible solution to open GUI application from web terminals?

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Author: Muhammad