It would be great to either have more granular editing of reminders from in-app (for example, when I click on the reminders icon, I can add notes), or some easy way to automatically open the Reminders app to the right reminder. Apologies if this functionality exists already… I know more than once I’ve suggested a “feature enhancement” only to find that you’ve solved for the problem already!
Allowing to add notes to a reminders from within a note taking app doesn’t make much sense IMO, it will likely confuse most users. Opening a reminder from within the app can be done on macOS by clicking the reminder in the calendar view in the inspector on the right. Unfortunately on iOS and iPadOS Apple removed this possibility in iOS13 
Thanks for the feedback, we’ll think about that, makes sense