I'm sure this is a stupid question. I started the 100 Days of SwiftUI course tonight. I downloaded "Developer" from the App Store on my iPhone but it does not have a playground. Do I have to have a Mac computer to take this course? No Windows compatible Developer version?

To write code that compiles and runs on iOS and Mac devices, the development environment (Xcode) needs access to application programming interfaces, aka APIs that execute code designed for iOS and MacOS.

For example, how might you display a Slider bar control in your application allowing your user to adjust their gaming chair's temperature?

Not Available

These APIs are not available on Windows platforms.

The application interface code for iOS is not the same as the code used to develop Windows programs. It might be similar, but it's not the same.

Cross Platform Development

There are a few solutions for developing iOS apps on Windows. You may want to look into google's Flutter language. They advertise that solutions written with flutter can run on both iOS and Android phones, and maintain the same look and feel.

The HackingWithSwift web site does not teach Flutter. You'll have more success at other teaching sites.