Importing WSL2 from my old laptop keeps reinstalling Ubuntu

I am attempting to configure a new laptop (Windows 10 Enterprise Version 20H2). I have installed WSL with the wsl --install command recommended by Microsoft.

I have managed to import a backup of my previous WSL2 Ubuntu 20.04 configuration and have set that as the default distribution.

PS C:WindowsSystem32> wsl --list --verbose
  NAME            STATE           VERSION
* Ubuntu-20.04    Stopped         2

However, when I attempt to launch Ubuntu (wanting my old config) from the launcher in the start menu, it installs a fresh version of Ubuntu and launches that

Installing, this may take a few minutes...
Please create a default UNIX user account. The username does not need to match your Windows username.
For more information visit: https://aka.ms/wslusers
Enter new UNIX username:

I’ve tried removing the unwanted instance with

PS C:WindowsSystem32> wsl --unregister Ubuntu

But the problem persists. So how can I get the launcher (or whatever the correct term is in Windows) to launch the default version?