I’ve read various suggestions that are similar to this but not this particular feature request. Simply put, to have a customization option (toggle in settings preferences) that allows one to “collapse note” whenever it is checked or “marked as done”. The idea here is that if it is completed, then it is unlikely to need to be fully open for reading and would thus declutter a long chain of notes. However, as indicated, if one likes to keep notes open, the option is aways to keep it that way (which is Agenda’s current state).
I see the rationale but am afraid that this is the kind of benefit that doesn’t weigh up against the feature bloat I’m afraid.