How can I learn IOS frameworks deeper?

I've been working with IOS for quite a while and I just can't seem to get past a certain level of complexity in my projects due to a lack of documentation available online. Now I'm working on a chart using apple's pretty fresh Swift Charts framework and I just can't get past a certain level of complexity in my chart, even though I went over pretty much all the available free and not free resources online. So, the question is where can I get enough knowledge to be able to make charts (and other UI) similar to those that developers at Apple make, and where do those developers get their information from and how much do I actually need to know to make similar stuff?