I've upgraded the kernel to 4.15 and now I can use the external monitor with the Lenovo X1 Carbon! Hooray! Thanks!
** Changed in: linux (Ubuntu) Status: Incomplete => Fix Released -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1763202 Title: Lenovo X1 Carbon 6th Gen. HDMI not working for external monitor To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1763202/+subscriptions -- ubuntu-bugs mailing list firstname.lastname@example.org https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs