Just completed ATLA. What is next in the series?

Korra is great, it had some issues from Nickeoldean that reduced its success. Basically they had no idea if there was going to be a season 2 or 3, so it was written that way. 3 and 4 are more connected.

There are 3 books series, each about Kyoshi, Yangchen and Roku (released in that order). Good books.

There are a lot of graphic novels for both Aang and Korra. I know they are free on webtoon and Hoopla (many libraries offer free acess to hoopla). (Webtoon doesn't have all of them yet, they've been regularly posting in the past year)

Netflix ATLA is a live acation remake made by different people. General option is meh, not as bad as the movie.

The movie is probably the worst movie released by a major studio, even by today's Netflix series wrecking standards.