Failed installing Ubuntu using termux-ubuntu
Here is the ubuntu.sh, you get an error because the disco image has been removed and the following URL doesn't download anything:
https://partner-images.canonical.com/core/disco/current/ubuntu-disco-core-cloudimg-${archurl}-root.tar.gz

Check the available images from this directory. Edit the ubuntu.sh by adding a valid URL. Here is an example using focal Codename. Replace the following line:
 wget &quot;https://partner-images.canonical.com/core/disco/current/ubuntu-disco-core-cloudimg-${archurl}-root.tar.gz&quot; -O $tarball

with:
wget &quot;https://partner-images.canonical.com/core/focal/current/ubuntu-focal-core-cloudimg-armhf-root.tar.gz&quot;  -O $tarball

or using the archurl variable:
wget &quot;https://partner-images.canonical.com/core/focal/current/ubuntu-focal-core-cloudimg-${archurl}-root.tar.gz&quot;  -O $tarball

Then run your script it should work as expected.