Lenovo ThinkPad X1 Extreme (Gen 3)
The Thinkpad X1E Gen 3 is workstation/multimedia laptop from Lenovo's 2020 ThinkPad X lineup.
See Laptop for generic laptop-related information, or ThinkPad for other ThinkPad laptops.
Secure Boot
    
Secure Boot with custom keys is fully and officially supported.
Install the sbctl package. In UEFI, enable Secure Boot and set Platform Mode to Setup Mode. Then, follow https://github.com/Foxboron/sbctl#key-creation-and-enrollment and https://github.com/Foxboron/sbctl#signatures.
Audio
    
    Built-in audio
    
This laptop requires firmware in order for the soundcard to work. See Advanced Linux Sound Architecture#ALSA firmware.
Blacklist the snd_hda_intel and snd_soc_skl modules.
Configure PulseAudio's to load Alsa modules with the correct device and  settings, by adding these two lines to :
load-module module-alsa-sink device=hw:0,0 channels=4 load-module module-alsa-source device=hw:0,6 channels=4
Unmute the Master channel:
$ alsamixer -c 0
Then press on your keyboard.
Video
    
The X1 Extreme comes with two graphics cards: the Intel CometLake UHD and Nvidia GeForce GTX 1650 Ti. The display is connected to the Intel card and the HDMI port is physically connected to the GeForce.
Xorg.conf with PRIME
    
Using the proprietary driver from NVIDIA, you can set the laptop to run on Intel and only use NVIDIA if triggered manually by running prime-run. To do so, the xorg.conf needs to explicitly define NVIDIA as a non–primary GPU:
Option "PrimaryGPU" "no"
No configuration for Intel is needed unless tweaking is required.
Follow PRIME for full featured setup.
Integrated webcam
    
The integrated webcam needs the uvcvideo kernel module to be loaded to work. See Kernel module for module-loading instructions.