If you want to avoid too much choice, but still want the "the past is immutable" feel, you can prevent editing after noon next day or similar.

Days "roll-over" when you sleep, so it should be safe to rollover notes which haven't been edited for 6 hours. That way there is no fixed rollover time.

Having the default "midnight" be something like 3AM would get you 90% there without any UI changes

I just use a .org file, with git to retain old versions if I edit something that might be of later relevance.