WSL needs to be the version of WSL from the Microsoft Store

WSL can be upgraded with wsl.exe --update in order for booting with systemd to work (also there's wsl --update --web-download), but it did pop up a UAC prompt even when the command was being run as Administrator, which doesn't bode well for automation.

This means the WSL that you get just from installing the Windows Feature isn't enough for it to work with systemd.