Should I use Swift or Objective-C to learn iOS development ?

The Swift programming language is the standard features rich language to create iOS apps, iPadOS apps and MacOS X apps. The present and the future is just Swift on Apple ecosystem.

Apple is perfecting Swift every year with updates and new features and capabilities. We are now in the era of SwiftUI, you should go for Swift already.

Swift itself is a robust programming language. So go for it! it is standard for hiring, learning, creating apps for Apple operating systems.