Good thing you noticed that! It appears to be a known SwiftUI bug, so, unfortunately, nothing you can do for now. But it may help if you scroll the view a bit and try to tap it again.
I believe this bug will be fixed when the next version of SwiftUI is released. It should happen after WWDC 2020.
For now, I’m working on the 3rd part of the tutorial, and once I’ve done, I’ll play a bit and try to find how to fix that and post an update if I succeed.