The definition of real time collaboration does vary widely from usecase to usecase and user to user. While the Joplin mobile app in theory does limit the minimum synch time to every 5 minutes there are (easy) ways to circumvent that and have a faster synch (I use every 60sec, but I selfhost).

Everything else you mentioned/require is available with Joplin. It literally has a checkbox Note-Type (but checkboxes can be easily added to every other note as well) which can easily be check off, Notes can be categorised into folders (Shared or not shared, with additional privacy locks available),etc.

Don't get me wrong, I have a myriad of ideas/things I would like to see Joplin do better. But its usability beats Google Keep - by far. And by now my extended family has adopted it - from an 8 year old to an 80 year old.