Ok. Thanks.
They have been, at least on Debian Buster for amd64 and armhf architectures. Just checked.
The Install script doesn't update minor version of nodejs. If you have a Pi2 or 3 then usual sudo apt update && sudo apt upgrade should do it as all we do is install the sources into /etc/apt/sources.list.d directory. For Pi0 and Pi1 (arm6) you may need to sudo rm /usr/bin/node /usr/bin/npm to remove (or hide) the existing nodejs then re-run our script which will then unpack the new version over the old one.
I solved this by logging into the container as root user:
docker exec -it -user root <container-ID> /bin/bash
and the ran:
npm i npm -g
It worked just fine.
