> But as I mentioned above, that makes the system more complicated for people who don't need it to be distributed. Setting up separate db software, configuring the connection, handling separate updates, etc. is a lot more work for most users than Jellyfin just using a local embedded sqlite database.

You can package a Postgres database with your app just like SQLite. Users should not have to know that they are using Postgres much less configuring connections, handling updates, etc.

> And it would probably make the application code more complicated as well.

Not at all, this is an article about the hoops the application has to jump through to make SQLite behave well with parallel access. Postgres is designed for parallel access by default. It’s strictly simpler from the perspective of the application.