Install Windows Subsystem for Linux and get error 0xc03a001a and a long list or question marks

I am following the steps on https://docs.microsoft.com/en-us/windows/wsl/install-win10 to install Windows Subsystem for Linux. Step 1 to 5 worked all well for me but in step 6 when I opened Ubuntu 20.04 downloaded from Microsoft Store, the following error occurred.

"WslRegisterDistribution failed with error: 0xc03a001a

Error: 0xc03a001a ???????????????????????????????????????????????????"

I saw other people having the same 0xc03a001a error but nobody got such a long list of question marks. Can anyone help me with that? Thanks a lot!

Not sure about the question marks, but they are likely obscuring the real error for some reason. "0xc03a001a" seems to typically correspond to "Virtual hard disk files must be uncompressed and unencrypted and must not be sparse." (See this Github issue along with others)

The solution for most people seems to be making sure that distribution folder is uncompressed. Quoting from this comment:

Essentially... find the package under C:\Users\AppData\Local\Packages and right click the folder, check advanced options and disable compression. Run the launch again.

• Of course ubuntu is listed under "CanonicalGroupLimited.Ubuntu" so if you sort alphabetically it will appear under "C"
• Debian is under "TheDebianProject" so that will appear under "T"