I'd say there's no quick way to do it, the message passing of obj-c is very different than the event-based slots & signals programming you are used to. And that's before the hell-which-is-InterfaceBuilder. Since you already familiar with programming, I'd suggest the Big Nerd Ranch guides at bignerdranch.com

Most online examples won't give you the details about the important stuff - single inheritance vs. categories, delegates and message passing in the runtime, extending a protocol, etc. You may see it in the code, but there won't be any theory or reasoning behind it to help you.

As a side note, you can track your learning progress by how much you hate XCode with specific examples of how it ruined your day.

Can't speak to clutch.io, but the other 2 just seem to get in the way of someone who already knows Ruby, C#, and obj-c. Do you really need another layer of abstraction if you want to learn something at a lower level?