An issue was discovered in Mbed TLS before 2.28.9 and 3.x before 3.6.1, in which the user-selected algorithm is not used. Unlike previously documented, enabling MBEDTLS_PSA_HMAC_DRBG_MD_TYPE does not cause the PSA subsystem to use HMAC_DRBG: it uses HMAC_DRBG only when MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG and MBEDTLS_CTR_DRBG_C are disabled.