On an API 29 Pixel 4 androidx.biometric.BiometricManager#canAuthenticate(Authenticators.BIOMETRIC_STRONG) returns BIOMETRIC_STATUS_UNKNOWN. I believe this is because the canAuthenticate(CryptoObject) method only works on Samsung devices - as far as I can tell it has never existed in AOSP.

Some possible solutions (there may well be reasons not to do these things):

Adding non-Samsung devices with strong face unlock to the assume_strong_biometrics_prefixes array, which is currently empty. Devices with fingerprint should be OK because they fall back to canAuthenticateWithFingerprintOrUnknown(), but I haven't actually tested this.
Attempt to create an auth-per-use key pair (setUserAuthenticationValidityDurationSeconds(-1)) in AndroidKeyStore, which fails with the following exception if the user doesn't have strong biometrics available & enrolled (I don't know if this is reliable across OEMs and API versions):

java.security.InvalidAlgorithmParameterException: java.lang.IllegalStateException: At least one biometric must be enrolled to create keys requiring user authentication for every use
        at android.security.keystore.AndroidKeyStoreKeyPairGeneratorSpi.initialize(AndroidKeyStoreKeyPairGeneratorSpi.java:349)
        at java.security.KeyPairGenerator$Delegate.initialize(KeyPairGenerator.java:697)
        at java.security.KeyPairGenerator.initialize(KeyPairGenerator.java:438)
        ...

BUILD INFO

Device type: Pixel 4
OS version: 10 (API 29)
Biometric library version: 1.1.0-beta01

STEPS TO REPRODUCE

Have API 29 Pixel 4 with face unlock turned on.
Call androidx.biometric.BiometricManager#canAuthenticate(Authenticators.BIOMETRIC_STRONG)

EXPECTED RESULTS

Receive BIOMETRIC_SUCCESS.

OBSERVED RESULTS

Receive BIOMETRIC_STATUS_UNKNOWN.

NUMBER OF TIMES YOU WERE ABLE TO REPRODUCE (e.g. 3/10)

10/10