ResizableTextView.swift

struct ContentView: View {
    var body: some View {
        VStack {
            Text("Hello, world!")
                .frame(maxWidth: .infinity, maxHeight: .infinity)

            ResizableTextView()
                .border(.red)
        }
        .padding()
    }
}

// this doesn't work when the text is wrapped
struct ResizableTextView: UIViewRepresentable {
    func makeUIView(context: Context) -> UITextView {
        let textView = UITextView()

        textView.font = UIFont.preferredFont(forTextStyle: .title1)

        // fit content
        textView.isScrollEnabled = false
        textView.setContentHuggingPriority(.defaultHigh, for: .vertical)

        // prevent expanding horizontally
        textView.setContentCompressionResistancePriority(.defaultLow, for: .horizontal)
        return textView
    }

    func updateUIView(_ uiView: UITextView, context: Context) {}
}