I'm Not sure it'll do those numbers. I really can't call it. People don't go to the cinema as much as they did in the past, yet Top Gun Maverick still made just shy of 1.5 billion at the box office, so who knows. Also, take into consideration that China was one of the reasons Avatar made so much money. The Chinese really love this franchise, so if it takes off in China then I can see it making 2B.
China B/O was no where near as big then as it is now. It only made 200 million at the time (not including re-releases, 260 with) which at the time was the best ever for a foreign film in China. Just a small piece of the 3 billion. If you don't include China, it still made over 2.7 billion. If you don't include the US or China, it still made over 2 billion elsewhere.
Since then in China it's been passed by Aquaman, Avengers (600 million), Fast & Furious, Transformers AOE, Venom, Zootopia, Jurassic World etc etc (not including re-release) due to how big China's market has become for movies since 2009.
This all favors Avatar 2. I see it ending up between 600-750 million in China, similar in the US. I don't see how it doesn't do 2 billion at this point w/ China in play.