Added test case that reproduces the reported bug.

Author: ekcoh

Assets/Tests/InputSystem/CorePerformanceTests.cs

@@ -126,7 +126,7 @@ public void Performance_ReadEveryKey()
             int keyIndex = 0;
             foreach (var key in keyboard.allKeys)
             {
-                if (++keyIndex == (int)KeyEx.IMESelected)  // Skip IMESelected as it's not a real key.
+                if (++keyIndex == (int)KeyEx.IMESelected)  // Skip IMESelected as it's not a real key. TODO This is incorrect, it should not even be there
                     continue;
                 key.ReadValue();
             }

Assets/Tests/InputSystem/CoreTests_Devices.cs

@@ -5894,4 +5894,18 @@ public unsafe void Devices_DoesntErrorOutOnMaxTouchCount()
                 BeginTouch(i, new Vector2(i * 1.0f, i * 2.0f), time: 0);
         }, Throws.Nothing);
     }
+
+    // Note: Tested inside this class for now since there are no dedicated device test classes for built-in devices,
+    //       only for plugin devices.
+    [Test, Description("https://issuetracker.unity3d.com/product/unity/issues/guid/ISXB-1541")]
+    [Category("Devices")]
+    public void Devices_KeyboardAllKeys_EnumeratesAllKeyControls()
+    {
+        var keyboard = InputSystem.AddDevice<Keyboard>();
+        int index = 0;
+        foreach (var key in keyboard.allKeys)
+        {
+            Assert.NotNull(key, $"Key at index {index++} was null");
+        }
+    }
 }