Before upgrading ePO - On-prem, back up your databases and directories to make sure you can recover your ePO - On-prem environment if the upgrade is unsuccessful.
Make sure that you have your Disaster Recovery snapshot passphrase. If you don't know it, see Change the server recovery passphrase.
Run a successful Disaster Recovery Snapshot server task. For details, see Disaster Recovery.
Back up all ePO - On-prem databases and directories. For details, see KB66616.