What I did: checked iCloud storage breakdown.
What happened: noticed Agenda occupied space both in my backup and in the sync area of iCloud.
What I expected: typically when enabling iCloud sync an app no longer needs to store content in the backup as this would be redundant.
Things that might be helpful to know (Agenda version, OS and model, etc): iOS 14.3, iPhone 12 Pro, Version 11.2
Reached out on Twitter initially. Seemed like a bug was encouraged to post my question here instead.