What do you mean by background sync, like it syncing as a background service without needing to open up the app?

Unfortunately, nested notebooks are still in the planning stage but they are on the road map. It's also something that I would really like to see added, but for right now since I get unlimited tags and notebooks and you can also select a couple of colors I've made a "tech" notebooks and made tags like "linux "lemmy" and things like that and then I can just stack the tags and if need be add a color to it to differentiate it further. I wouldn't say that Joplin is bad just that leaves a lot to be desired and especially things that I really need for my day to day and just like that is integrated to notesnook. Right now they're almost done with adding different app formats but nested notebooks is pretty soon on the list