I am using a new Thinkpad X1 Titanium Yoga with an integrated Intel Iris Xe and an i5 processor (11th Gen, 1140G7). I've tried Ubuntu 20.04 LTS and 21.04 without further changes, and currently use Pop!_OS 20.10.

Unless I boot with the additional nomodeset kernel option the screen stays black. Irrespective of that, performance is sub-optimal. Hardware accelerations seems off.

I tried different Kernels. So far no success. This is the output of inxi:

shess@pop-os:~$ inxi -G

Graphics:

  Device-1: Intel driver: N/A 

  Display: x11 server: X.Org 1.20.9 driver: fbdev unloaded: modesetting,vesa 

  resolution: 2256x1504~95Hz 

  OpenGL: renderer: llvmpipe (LLVM 11.0.0 256 bits) v: 4.5 Mesa 21.0.0 

shess@pop-os:~$ uname -r

5.10.0-1023-oem

I successfully solved the problem. See my own answer below.