Objective-C
Objective-C was created in 1984 as an extension of C. It added Smalltalk style messaging and Object Orientation to the C language. It was the standard programming language on macOS and iOS until the introduction of Swift in 2014.
Why is this technology on hold?
Swift is now pretty stable and has been the constant focus of Apple with continuous language improvements, exclusive revolutionary new frameworks like SwiftUI and Combine. Community efforts today are pretty much all around Swift.
Apple continues to offer great interoperability between Objective-C and Swift and will not abandon support for Objective-C anytime soon, but at this point migrating from Objective-C to Swift is definitely worth the investment.
Related technologies
Swift
Adopt
Swift is a general-purpose, multi-paradigm, compiled programming language developed by Apple Inc. It's most commonly used for developing iOS, iPadOS, macOS, watchOS and tvOS application.
Apple intended Swift to support many core concepts associated with Objective-C, notably dynamic dispatch, widespread late binding, extensible programming and similar features, but in a "safer" way, making it easier to catch software bugs; Swift has features addressing some common programming errors like null pointer dereferencing and provides syntactic sugar to help avoid the pyramid of doom. Swift supports the concept of protocol extensibility, an extensibility system that can be applied to types, structs and classes, which Apple promotes as a real change in programming paradigms they term "protocol-oriented programming".
Source: Wikipedia