On a work computer I'm currently using WSL quite often and thus wanted to see if there is a pbcopy/pbpaste equivalent.
Turns out WSL integrates with the X11 and Wayland clipboard APIs, thus we can simply install wl-clipboard.

With this in place, running wl-paste inside WSL dumps the content of the Windows clipboard.
And echo "foobar" | wl-copy puts "foobar" into the Windows clipboard.