I resolved my issue. My problem wasn’t that I wanted to create a database in my default environment - I was just trying to experiment with the new flow capabilities. What I hadn’t realised is that you need to be conscious of the environment you are working in - the magic happens just under your profile details (screenshot below). Once I selected an appropriate environment (you can’t use your default) every lit up and I could continue my studies.
However, IMHO the UI here is very confusing here, rather than saying "create a database" (which depending on your environment you can’t) it would be much better saying something like "select another environment, create a new environment or create a new database (if you are in a suitable environment and no database has been provisioned)" - hope this helps others who are similarly confused.
Flow Environment Selector