I'd like to say neovim but if notepad++ is too complicated then neovim definately is. There are 'distributions' that give you a setup ready to go e.g. Lazyvim but you're still going to have to fiddle with it sometimes.

https://www.lazyvim.org/

I don't think Lazyvim has any ai features out of the box.

If you are at all curious the 'Lazyvim for Ambitious Developers' book is a great way in and easy to skim through. Here's the chapter on ai which proves you have to turn it on to enable it:

https://lazyvim-ambitious-devs.phillips.codes/course/chapter-16/

I can't say for sure if the developers of neovim are using ai themselves for the codebase, I suspect they might be as they have made positive statements on it in the past. Love to hear if someone can confirm or not.