Supposedly all of WB's 2021 theatrical releases, although we'll see if that actually happens after all the pushback from directors, actors, theaters, etc.
There's a lot of pushback, but there's nothing directors, etc. can do. That said, Legendary Entertainment financed about 75% of Dune and they're supposedly trying to challenge Warner's decision. However, they also financed about the same amount of Godzilla vs. Kong and WarnerMedia (parent company of Warner Bros.) blocked them from selling it to Netflix for about $250 million. Legendary is especially pissed because Warner let them know about the HBO Max decision only about 30 min before their public announcement (probably because they were afraid of the news leaking early).
It's an uphill battle, though. Remember-- AT&T owns WarnerMedia, which owns Warner Bros., and--wait for it...HBO Max. AT&T is fighting to survive. As of the end of 2019, they held $150 BILLION in debt, and obviously, the pandemic hurt them even more. Their stock price is down over 20% over the past year. HBO Max's launch has so far been abysmal, so they decided to sacrifice Warner Bros.' entire 2021 slate as a desperate act to make a huge splash with the audience and prop up HBO Max. They know that even though many theaters are open, it's still less than half of them, and much of the audience will still avoid going because they don't feel safe.
AT&T felt this was the best choice of a bunch of shitty options.