For iOS15
There is a solution implemented by apple (as mentioned by @AlphaWulf)
For iOS14
In my opinion, the best approach is to implement your own version of TextField using the UIRepresentable protocol. This might sound like something difficult but it is actually quite simple.
Why it is better to implement your own text field over the solutions using view hierarchy introspection?
One is that a solution based on traversing underlying views is hacky by nature and even a minor iOS version update might break it.
Secondly, in a real-world app, you will want to set additional things on the text field (like return button type and supplementary view) but Apple didn't make a way of doing so and you will be forced to wrap a UITextField in any case.
https://blog.agitek.io/swiftui-2-first-responder-b6a828243268
In this post I have a detailed solution that is similar to what Apple has implemented in SwiftUI 3.