setIsStrongBoxBacked() for doesn't throw StrongBoxUnavailableException as expected

Question

Im recently working with Android keystore system.

A Xiaomi 9 phone and Huawei P20(updated to Android 9) were used for test which might not support StrongBox according to the GrapheneOS/AttestationSamples provided from this link.

Furthermore, below code returned false indicate that the device doesn't have StrongBox Feature.

private boolean hasStrongBox(Context context){
    return context.getPackageManager().hasSystemFeature(PackageManager.FEATURE_STRONGBOX_KEYSTORE);
}

However, during the test, when I'm generating AES encryption key by using the code below , both of the phone doesn't throw StrongBoxUnavailableException:

protected int createAndroidKeyStoreSymmetricKey() throws NoSuchProviderException, NoSuchAlgorithmException, InvalidAlgorithmParameterException {
    KeyGenerator keyGenerator = KeyGenerator.getInstance(KeyProperties.KEY_ALGORITHM_AES, "AndroidKeyStore");

    KeyGenParameterSpec.Builder builder = new KeyGenParameterSpec.Builder(ALIAS_MASTER_KEY, KeyProperties.PURPOSE_ENCRYPT | KeyProperties.PURPOSE_DECRYPT)
            .setBlockModes(KeyProperties.BLOCK_MODE_CBC)
            .setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_PKCS7);
            .setIsStrongBoxBacked(true);
    
    keyGenerator.init(builder.build());
    secretKey = keyGenerator.generateKey();

    if(secretKey != null ){
        return 0;
    } else {
        return -1;
    }
}

While generating RSA encryption key, they both did throw StrongBoxUnavailableException:

private KeyPair genKeyPair(String alias, boolean isStrongBoxBacked) throws Exception {
    KeyPairGenerator kpg =
            KeyPairGenerator.getInstance(KeyProperties.KEY_ALGORITHM_RSA, "AndroidKeyStore");
    KeyGenParameterSpec.Builder keyBuilder = new KeyGenParameterSpec.Builder(
            alias,
            KeyProperties.PURPOSE_ENCRYPT | KeyProperties.PURPOSE_DECRYPT)
            .setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_RSA_PKCS1)
            .setBlockModes(KeyProperties.BLOCK_MODE_ECB)
            .setKeySize(CRYPTO_BITS)
            .setIsStrongBoxBacked(true);
    kpg.initialize(keyBuilder.build());

    return kpg.generateKeyPair();
}

android.security.keystore.StrongBoxUnavailableException: Failed to generate key pair

Is there any spec configuration was done wrong during the Key generation? As The expecting result is StrongBoxUnavailableException is thrown even during the AES generation.