During the application of a .PAK file of a stand alone Aria Operations instance under Update Information step 2 of the Add Software Update wizard it shows:
2. Run the pre-upgrade assessment tool before the upgrade. This is imperative and will provide you with a list of impacted content caused by the removal of numerous metrics from the product. Ignoring this step may potentially lead to broken content.
VCF Operations 9.1.0.0400
Aria Operations 8.18.5
The Pre-Upgrade Assessment tool is not available for VCF 9.1 standalone upgrades and this message can be ignored.
Be sure to have backups, snapshots, and content backups available of any custom content prior to the upgrade as outlined in Upgrading to VMware Cloud Foundation 9.1