This is similar to DOCS-6709.

As best practice, backing up the Ops Manager backing databases should be recommended prior to an upgrade. The recommendation could be made in this documentation, since in the 3.4 case it mentions that there are no downgrade paths.

• 3.4 - https://docs.opsmanager.mongodb.com/v3.4/tutorial/nav/upgrade-application/
• 2.0 - https://docs.opsmanager.mongodb.com/v2.0/tutorial/nav/upgrade-application/

A link to the procedure to perform the backup of the backing databases should be included, which I believe is here:
https://docs.opsmanager.mongodb.com/current/tutorial/backup-the-backup-service/#shut-down-and-back-up
(The emphasis there seems specific to snapshots, so it may need to be generalized and/or link to
https://docs.mongodb.com/manual/tutorial/backup-with-filesystem-snapshots/).