There seems to be a much easier answer to this, at least on windows 11 if your not really wanting to run around with powershell commands in your head.
Basically, install a distro. For example:
wsl --install -d Ubuntu
Unregister it:
wsl --unregister Ubuntu
This deletes your "root" drive as such, but doesn't remove the ubuntu image.
Go to Settings > Apps > Apps & Features, search for ubuntu, then click on the three dots button next to the result, should look something like this:

Click on move, then just choose the drive.... go to the start menu (or hit the windows key or whatever works for you), search for ubuntu and run it which kicks off the installer.
Everything it does will now be on the drive you chose including the running disk image.