Unable to resolve 'download.nodesource.com'
Looks like NodeSource has removed their DNS record for the "download" subdomain. This means you'll need to remove (or disable) the repository from your sources list.
Assuming you're using the Desktop version of Ubuntu, you can do it like this:
- Open "Software & Updates":
- Select the "Other Software" tab:
- Uncheck the record for download.nodesource.com
- Press "close" and update apt