Yeah if you put the tags in the content of the posts they will get indexed and search should find them, keep in mind the body of the posts are searched when you search in "posts" so if you are only searching for titles they wont show up.
We use NodeBB also as a CMS containing English definitions on a dictionary. Our users are loving it. but we are struggling in increasing our Google rankings as all our competitors are using AMP pages to outrank us.
We would need an official Google AMP plugin that would enable any node bb topic page , like the 1 I'll post my topic on, to have an alternative Accelerated Mobile Page. https://amp.dev/
Since when each topic will have a corresponding AMP version then it will help us rank much more easily in Google SEO search results and increase our rankings.
With this plugin, our users can help us discover our sites and node bb itself site much more easily because Google ranks AMP pages better and higher over normal html pages.