When VoiceOver's typing mode is touch typing
When a finger touches the TextField and lets go, it will activate the TextField by mistake, causing the keyboard to pop up.
If you change VoiceOver's typing mode to standard typing, you won't have this problem.
But in native typing mode, no matter what type mode you touch the TextField and let go, the popup control is not activated unless the user manually double-clicks the screen.
Note: Steps for modifying different typing modes:

1. Open VoiceOver.
2. Find an input box and pop up the keyboard.
3. Use the rotor gesture (press one finger on the screen and rotate the other finger around it), then release your hand when you hear "typing mode".
4. Swipe a finger down on the screen and you'll hear three different options: Standard type, Touch Type, and Direct Touch Type.

Since I don't speak English, I use a translator, so the description may not be completely accurate, if you have any questions, please comment!

This is my code snippet:
TextField(
decoration: InputDecoration(
labelText: "user name",
hintText: "user name or email",
prefixIcon: Icon(Icons.person)
)),

I use：
Flutter (Channel beta, 2.7.0-3.1.pre