I've used a similar approach before, and for me it worked like this:
I have an article about database programming in Python which has neo4j example code. In Joplin I've added these tags (here the comma is the tag separator):
Python, database, neo4j
If I had nested tags, that would become:
python / database / neo4j
The first approach needs the equivalent of a database join to find the article, the latter is a hierarchy which makes the finding easier. The more articles you have the more useful hierarchic or nested tags can become.
With nested tags, for similar articles I could also have:
python / database /cockroachdb
python / database / mssql
python / database / sqlite
and so on.