This seems obvious, but I've been learning Swift myself, and I've found that the official book you can find on the Swift website is pretty easy to follow. It does require some other Programming experience to really get the most out of it, but I've found it fairly accessible overall.
Description: Free online course that teach Swift over 100 days, starting with the basics of Swift for the first 14 days, then dives into several mini projects each teaches you something new in a practical way. Note that this course uses UIkit for GUI instead of the new SwiftUI.
Title: 100 Days of Swift UI (made by Hacking with Swift)
Author: Paul Hudson
Description: A free collection of videos, tutorials, tests, and more all designed to help you learn SwiftUI effectively. It’s aimed squarely at beginners who want to learn to build real iOS apps, but struggle to find a good, free course that can help them achieve their goals. If that’s you, welcome – I hope you’re ready to show the iOS world what you’re made of!