@dazinism Hey, thanks again. I've tried Tasks, it doesn't have the right UX.
Google extended Google Calendar to have something called Reminders, which are sort of like Events but not really, thus not caldav compatible.
None of the f-droid To-Do/Task apps I've tried replicate the UX of gcal Reminders. "Repeat Me" is closest, but it's beta quality and buggy.
I suspect the answer is either in a reminder app I haven't yet found, or it doesn't exist.