I tried plugin install via cmd line as per doc.nodebb guide linked above does not seem to have worked.
Terminal spit this out (removed code)
UPDATE: Tried it again, using historical advice from @The-Worms (back up the thread - click here) this time using
sudo npm remove nodebb-plugin-ns-embed
npm install nodebb-plugin-ns-embed
Now I can see the plugin with nBB v1.12.2 and it works too + to have everything in one place next time I forget what I did or anyone else, here is the Twitter code that works for custom embed.
<blockquote class="twitter-tweet"><a href="https://twitter.com/$1/status/$2?ref_src=twsrc^tfw"></a></blockquote> <script async src="https://platform.twitter.com/widgets.js" charset="utf-8"></script>