"Unable to locate package" for exa on WSL 2 Ubuntu

The groovy name is 20.10, not 20.04 LTS. So this package is not available for 20.04 LTS.

But you can install it manually with:

wget -c http://old-releases.ubuntu.com/ubuntu/pool/universe/r/rust-exa/exa_0.9.0-4_amd64.deb
sudo apt-get install ./exa_0.9.0-4_amd64.deb

and test it via:

$ exa --version
exa v0.9.0