Running npm run build with the default template will not output anything if the manifest.json is not in the correct format (for example: a trailing comma).

I know javascript as a whole is a joke but could their devs at least try to make it remotely bearable ?

By the way, background scripts don't work if the source file isn't located in the scripts folder which is very misleading with this:

Place any additional background scripts that are not directly declared in manifest.json into the /scripts folder.