ヽ｜∵｜ゝ(Fantom) の 開発blog？

using UnityEngine;
using UnityEditor;
using UnityEditor.Build;

//※Editor フォルダに配置
public class EditorPlatformSetting : IActiveBuildTargetChanged, IPreprocessBuild  //※クラス名は任意
{
    public int callbackOrder => 0;

    //ビルドターゲットを変更したときのコールバックハンドラ
    public void OnActiveBuildTargetChanged(BuildTarget previousTarget, BuildTarget newTarget)
    {
        Debug.Log("BuildTarget is " + newTarget);
        ForceRunInBackgroudIsTrueIfNeeded(newTarget);
    }

    //ビルド開始するときのコールバックハンドラ
    public void OnPreprocessBuild(BuildTarget target, string path)
    {
        ForceRunInBackgroudIsTrueIfNeeded(target);
    }

    //プラットフォームにより、強制的に RunInBackgroud をオンにする
    void ForceRunInBackgroudIsTrueIfNeeded(BuildTarget target)
    {
        switch (target)
        {
            case BuildTarget.StandaloneWindows:
            case BuildTarget.StandaloneWindows64:
            //※必要なら、プラットフォームをここに追加する
                Debug.Log("Force RunInBackgroud to True");
                Application.runInBackground = true;
                break;

            case BuildTarget.Android:
                //※Android では無視される
                break;
        }
    }
}

using System;
using UnityEngine;

#if ENABLE_INPUT_SYSTEM
using UnityEngine.InputSystem;
#endif

public class AndroidBackKeyTest : MonoBehaviour
{

#if ENABLE_INPUT_SYSTEM

    public Key targetKey = Key.Escape;
    public KeyCode targetKeyCode = KeyCode.Escape;

    // Use this for initialization
    private void Start()
    {
        Debug.Log($"Platform : {Application.platform}");
        Debug.Log($"SystemInfo.operatingSystem : {SystemInfo.operatingSystem}");
    }

    bool keyPressing;
    bool keyCodePressing;
    float keyPassedTime;
    float keyCodePassedTime;

    // Update is called once per frame
    private void Update()
    {
        if (Keyboard.current[targetKey].wasPressedThisFrame)
        {
            keyPressing = true;
            keyPassedTime = Time.time;
            Debug.Log($"<color=cyan>[frame:{Time.frameCount}][passed:0.000] [{targetKey}].wasPressedThisFrame</color>");
        }

        if (Input.GetKeyDown(targetKeyCode))
        {
            keyCodePressing = true;
            keyCodePassedTime = Time.time;
            Debug.Log($"[<color=cyan>frame:{Time.frameCount}][passed:0.000] GetKeyDown({targetKeyCode})</color>");
        }

        if (keyPressing)
        {
            if (Keyboard.current[targetKey].isPressed)
            {
                Debug.Log($"[frame:{Time.frameCount}][passed:{(Time.time - keyPassedTime):F3}] [{targetKey}].isPressed");
            }

            if (Keyboard.current[targetKey].wasReleasedThisFrame)
            {
                Debug.Log($"<color=magenta>[frame:{Time.frameCount}][passed:{(Time.time - keyPassedTime):F3}] [{targetKey}].wasPressedThisFrame</color>");
                keyPressing = false;
            }
        }

        if (keyCodePressing)
        {
            if (Input.GetKey(targetKeyCode))
            {
                Debug.Log($"<color=#999999>[frame:{Time.frameCount}][passed:{(Time.time - keyCodePassedTime):F3}] GetKey({targetKeyCode})</color>");
            }

            if (Input.GetKeyUp(targetKeyCode))
            {
                Debug.Log($"<color=magenta>[frame:{Time.frameCount}][passed:{(Time.time - keyCodePassedTime):F3}] GetKeyUp({targetKeyCode})</color>");
                keyCodePressing = false;
            }
        }
    }

#endif

}

bool keyPressing;

private void Update()
{
    if (Keyboard.current[targetKey].wasPressedThisFrame)
    {
        keyPressing = true;
        //押したときの処理
    }

    if (keyPressing)
    {
        if (Keyboard.current[targetKey].wasReleasedThisFrame)
        {
            //離したときの処理
            keyPressing = false;
        }
        else
        {
            //継続中の処理
        }
    }
}