Postgres even supports using NoSQL concepts with JSONB so there’s no reason not to start with it.
I’m sure I’ll get downvoted since HN has been very hostile to real talk lately but I don’t care.
As for NoSQL. I'd say that definitely should be on the roadmap. I've assumed that they've already learned RDBMS, but knowing when to use the two is essential. Most companies now are working with data lakes and unstructured data (e.g. user and session data). Knowing how to get around that flexibility, how to structure your business logic and models, and what tool to pick (i.e. Redis for caching), etc. goes alongside NoSQL knowledge.
I had a bad experience with a project that I was assigned to "help". The build steps documented used incompatible lib version. It's hard to help if you can't even build/run their codes.
NoSQL databases are just a tool like other tools. And you should know when and why to apply such tools not just dismiss learning them altogether.
Also every developer goes on their own journey. So if someone wants to build a social network then a graph database is going to make more sense even at the beginning than a relational one.