bin contains certain system app binaries, /boot contains the files required for Ubuntu to boot up, /dev contains special files that symbolize hardware like your hard drive, while /etc contains ...
If you run into problems, check your USB drive's S.M.A.R.T health and confirm that you've selected the right file system ...
Starting from WSL version 2.4.8, we can install Ubuntu on WSL from a tar file, without using the Microsoft Store on Windows.