I've looked around quite a bit at the EventKit documentation and done all the searching I could think of, as well as examining the EKCalendar and EKEventStore types. Trying to find out how to view, modify, and create groups of reminders lists.
EventKit Reminders Groups?
It's not currently possible to view, modify, and create groups of reminder lists through EventKit. The best way to request this functionality is to file a Feedback Assistant with this enhancement request.
EventKit genuinely doesn't expose sections (or their subsets/groups). The only working approach I've found is to bridge to the Reminders SQLite store and handle the CloudKit sync manually, which took some reverse-engineering of how remindd works. I documented what I learned while building remi (https://github.com/mattheworiordan/remi), a CLI for Reminders: https://github.com/mattheworiordan/remi/blob/main/docs/APPLE_REMINDERS_INTERNALS.md