Followed (kind 3) and Muted (kind 10000?) work just like custom lists, except you cannot rename them or delete them. You can add as many custom lists as you want. You can add new npubs to them. You can also go to a person page and flip switches to add/remove the person from any of your lists. And you can mark people as "private" on a list so when published it hides the fact they are on the list by putting them in the encrypted contents.

I will do a short video on it I think.