谢谢你的指点@pskink -这为我解决了问题：

class LoginHandlerWrapper extends StatefulWidget {
  final Widget child;

  const LoginHandlerWrapper({super.key, required this.child});

  @override
  State<LoginHandlerWrapper> createState() => _LoginHandlerWrapperState();
}

class _LoginHandlerWrapperState extends State<LoginHandlerWrapper> {
  bool absorbPointer = false;

  @override
  Widget build(context) {
    return Listener(
        onPointerDown: (event) {
          if (FirebaseAuth.instance.currentUser?.isAnonymous == true) {
            showModalBottomSheet(
                context: context, builder: (context) => const SignIn());
            setState(() {
              absorbPointer = true;
            });
          } else {
            setState(() {
              absorbPointer = false;
            });
          }
        },
        child: AbsorbPointer(
          absorbing: absorbPointer,
          child: widget.child,
        ));
  }
}