Install 19.04 on ThinkPad X1 Extreme Gen 2
Solution 1:
I received my Extreme Gen 2 on the October 31st 2019, I did not install Ubuntu 18.04 because I would not be able to upgrade the kernel version without WiFi since I don't have Ethernet port.
Consequently I installed Ubuntu 19.10 (kernel 5.3), disabled Secure Boot, Windows fast startup and blacklisted the NVIDIA Nouveau driver to replace it by the proprietary NVIDIA Driver. Now everything works even Docker.
Here are the steps to install it along Windows:
Disable Windows 10 fast startup because when it is enabled, your computer doesn’t perform a regular shut down: instead it builds hibernation files that you want avoid when dual-booting.
Update UEFI/BIOS to 1.26 (initially my UEFI/BIOS was up to v1.17) since old UEFI/BIOS contain multiple bugs that can result in bricking the laptop. You can perform it using the Lenovo Vantage app under Windows 10.
Disable Secure Boot: it is a verification mechanism for ensuring that code launched by a computer’s UEFI firmware is trusted. The issue is that NVIDIA Drivers are not signed hence Secure Boot would interrupt the boot process.
Install Ubuntu by hitting Enter on startup and selecting your bootable USB stick. Now you have Ubuntu installed on your laptop but it crashes when loading the default Ubuntu’s Nouveau NVIDIA Driver. Consequently we will blacklist it and installing the NVIDIA proprietary driver which works fine.
Reboot the computer. In the GRUB menu press E to edit the command before booting then append ‘nomodeset’ at the end of the ‘linux…’ line : it will prevent the system from loading graphics drivers hence we will be able to install NVIDIA drivers and blacklisting the Nouveau driver. Don’t worry, ‘nomodeset’ will only be effective for that session.
Install last NVIDIA proprietary driver.
Blacklist Nouveau driver to avoid conflicts.
Now the NVIDIA proprietary drivers are installed on your system and the open-source Nouveau driver is blacklisted so no conflicts between graphics drivers should happen.
These instructions come from the Medium article I wrote (https://medium.com/@remy.hosseinkhan/installing-ubuntu-19-10-on-lenovo-thinkpad-x1-extreme-gen-2-and-p1-gen-2-ba4c9c7c7ed2) check it if you have trouble to solve one step. I've looked at several threads in order to understand what goes wrong with installing Linux on this laptop : the main issue comes from the NVIDIA Optimus technology that is still causing trouble nowadays (see Is a NVIDIA GeForce with Optimus Technology supported by Ubuntu?).
Solution 2:
As I just got a Lenovo ThinkPad X1 Extreme Gen 2 today and immediately wiped the drive and tried to install Ubuntu and ran into some problems I thought I'd offer my solution (which wasn't possible at the time of OP's post, but from the comments they seem to have also come to) in the event that someone like me might need a much more detailed explanation.
I originally tried to install Ubuntu 18.04.3 LTS but soon found that there was no Wi-Fi adapter found at all. After checking the X1's tech specs again I searched on "Intel AX200 Wi-Fi 6 802.11AX" and found the Linux* Support for Intel Wireless Adapters page which listed the Intel Wi-Fi 6 AX200 160MHz as needing a Linux kernel release of 5.1+. As uname -r showed that 18.04.3 had 5.0, after checking the Ubuntu releases it was clear that (in October of 2019) the only viable option was Ubuntu 19.10 (as it had kernel 5.3). Doing a clean install of 19.10 immediately fixed the Wi-Fi problem, but then during the gnome-initial-setup (Welcome to Ubuntu) the entire OS would freeze up. I noticed that before continuing with the gnome-initial-setup that if I looked around in settings that I found that the default graphics driver being used was the Nouveau and not the Nvidia (proprietary, tested) driver. If the Nvidia driver was switched to and then the gnome-initial-setup was run it would complete without issue and the computer was finally ready for use.
While I now quite happy so far with Ubuntu 19.10 and the Lenovo ThinkPad X1 Extreme Gen 2, I am certainly looking forward to the 20.04 LTS release in 2020.