Banned User

What can he do if a user is banned? And are browsing differences still work?

probably still can visit Danbooru but unable to do anything, since they are banned.

From screenshots I've seen from banned users, most read-only actions still work, there's just a giant banner at the top telling you about your ban, and you obviously can't actually interact with anything.

Creating and modifying favgroups is about the only available feature since nothing can be favorited or voted on