It bothers me how job ads tend to focus on various buzzwords. I'm quite sure you're better off hiring someone with good fundamentals who can learn your stack, rather than someone who is a novice but has some experience in the stack.
I started off doing financial trading code in c++ / c#. It wasn't a huge leap doing Android and iOS. Principles are the same:
- Some kind of OO. They are all pretty similar for most purposes. C++ is maybe a bit more intricate. Similarly, some kind of functional/lambda.
- Some way to access a database. Plenty of ORMs or ways to do SQL if you need that.
- Some GUI organisational principles. WinForms, WPF, Qt, Android, iOS, whatever. They tend to have things like "only draw on the main thread" and a pile of APIs for organising the screens, buttons, and so forth. But if you've done one, you're not going to need a course to do another.
- StackOverflow will tell you everything that's pure translation. Things like {} dicts for python.
- Get a brief tutorial for each new language/framework. They're all over the web, and the main point it just to highlight the features.