Maybe the system is remembering the external monitor as a configuration where the laptop screen was once turned off. So switching to that configuration involves turning off the laptop screen. To fix that try deleting all memory of the monitor configurations:
rm ~/.config/monitors.xml ** Package changed: xorg (Ubuntu) => mutter (Ubuntu) ** Tags added: multimonitor ** Changed in: mutter (Ubuntu) Status: New => Incomplete -- You received this bug notification because you are a member of Ubuntu Desktop Bugs, which is subscribed to mutter in Ubuntu. https://bugs.launchpad.net/bugs/1903829 Title: laptop screen turns off when I connect an external monitor To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/mutter/+bug/1903829/+subscriptions -- desktop-bugs mailing list desktop-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/desktop-bugs