We use the
gcloud app deploy --service-account=SERVICE_ACCOUNT_NAME@PROJECT_ID.iam.gserviceaccount.com
@Aditya Ekbote hi. According to your link provided:
This feature is covered by the Pre-GA Offerings Terms of the Google Cloud Terms of Service. Pre-GA features might have limited support, and changes to pre-GA features might not be compatible with other pre-GA versions.
We will discuss inside a team about what we can do and provide you results.