大部分代码都是一样的。我对代码做了一些修改，它可以做你想要的事情。逻辑很简单，如果按键被按下，它会检查哪个按键被按下，哪个节点有焦点，然后根据这个来改变焦点。另外，你检测按键的代码在我的系统上不起作用，所以我根据我的系统修改了它，但是你可以把它改回你想要的按键。
产品代码：

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatefulWidget {
  const MyApp({super.key});

  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  FocusNode? f1, f2, f3;

  leftKeyPressed() { // check which node has focus
    if (f2!.hasFocus) {
      FocusScope.of(context).requestFocus(f1);
    } else if (f3!.hasFocus) {
      FocusScope.of(context).requestFocus(f2);
    }
  }

  rightKeyPressed() { // check which node has focus
    if (f1!.hasFocus) {
      FocusScope.of(context).requestFocus(f2);
    } else if (f2!.hasFocus) {
      FocusScope.of(context).requestFocus(f3);
    }
  }

  void _onFocusChanged1() {
    setState(() => f1?.hasFocus ?? false);
  }

  void _onFocusChanged2() {
    setState(() => f2?.hasFocus ?? false);
  }

  void _onFocusChanged3() {
    setState(() => f3?.hasFocus ?? false);
  }

  @override
  void initState() {
    super.initState();
    if (f1 == null) {
      f1 = FocusNode();
      f2 = FocusNode();
      f3 = FocusNode();
      f1?.addListener(_onFocusChanged1);
      f2?.addListener(_onFocusChanged2);
      f3?.addListener(_onFocusChanged3);
      f1?.requestFocus();
    }
  }

  @override
  void dispose() {
    f1!.dispose();
    f2!.dispose();
    f3!.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: SafeArea(
          child: RawKeyboardListener(
            focusNode: FocusNode(),
            onKey: (event) {
              if (event.runtimeType == RawKeyUpEvent) {
                if (event.logicalKey.keyLabel.toString() == "Numpad 4") { // check which key is has focus. "Numpad 4" is the left arrow key in my system.
                  leftKeyPressed();
                } else if (event.logicalKey.keyLabel.toString() == "Numpad 6") { //"Numpad 6" is the right arrow key in my system.
                  rightKeyPressed();
                }
              }
            },
            child: Center(
              child: Padding(
                padding: const EdgeInsets.all(16.0),
                child: Row(
                  mainAxisAlignment: MainAxisAlignment.spaceBetween,
                  crossAxisAlignment: CrossAxisAlignment.center,
                  children: [
                    Focus(
                      focusNode: f1,
                      child: Container(
                        padding: const EdgeInsets.all(16),
                        height: 100,
                        width: 100,
                        color: (f1?.hasPrimaryFocus ?? true)
                            ? Colors.red
                            : Colors.blue,
                      ),
                    ),
                    Focus(
                      focusNode: f2,
                      child: Container(
                        padding: const EdgeInsets.all(16),
                        height: 100,
                        width: 100,
                        color: (f2?.hasPrimaryFocus ?? true)
                            ? Colors.red
                            : Colors.blue,
                      ),
                    ),
                    Focus(
                      focusNode: f3,
                      child: Container(
                        padding: const EdgeInsets.all(16),
                        height: 100,
                        width: 100,
                        color: (f3?.hasPrimaryFocus ?? true)
                            ? Colors.red
                            : Colors.blue,
                      ),
                    ),
                  ],
                ),
              ),
            ),
          ),
        ),
      ),
    );
  }
}

输出：-