Hmm, well – Objective-C holds a place in my heart. It's not for everyone, but it's really where I got my start and I think it's a beautiful language and had an incredibly unique community around it that started with all the NeXT folks.
I'd be curious why Objective-C now? Still has its place for some things. It's interoperability with C++ for instance, especially if you're dealing with things like Metal or certain real time audio libraries.
It's also probably a niche in terms of maintaining legacy stuff. Like being a Fortran developer and having your pick of contracts because nobody remembers it anymore and some crucial piece of infra relies on it.
But, Big Nerd Ranch guid is how I learned! And again, by doing projects. Just pick something you want to build with it and see it through to the end. Like writing, it's best to plough through and just get SOMETHING that works end to end, knowing that it'll be your first draft and you'll get it better on the second Tim around.
Good luck!