I have a fresh Windows 10 2004 (20170.1000) system with an Ubuntu 18.04.4 WSL2 instance. Following the instructions in the CUDA WSL2 user guide everything is fine until the section Install NVIDIA Container Toolkit. I get the following errors when I try to add the repositories.
# Unsupported distribution!
# Check https://nvidia.github.io/nvidia-docker
Figured out the issue. May have been two unrelated ones, realizing there is a period in this command fixed the immediate issue:
distribution=$(. /etc/os-release;echo $ID$VERSION_ID)
But also that the kernel needs to be 4.19.121 or higher. In order to upgrade the kernel in WSL you must tell Windows Update to receive updates for other Microsoft products. The default is turned off for this setting.