In general, I don't suggest that people become language masters before starting with frameworks (this might be controversial).
But they should learn both the framework and the language (possibly simultaneously).
You can't really understand what's going on with the framework if you don't understand the language. That's only acceptable if you're a beginner and still actively working on learning it.
There are limits though. Some things are abstracted away well enough by good frameworks (although it always helps to know). You probably don't know how the framework does sockets for traditional pages, you might skip async if your framework doesn't use it, and you could delay learning SQL for some months with a good ORM. But you'll need to dig deeper to reach a higher level.