Dune would need to make ≈2.7x it's first week to reach $300m. There are 121 films which have had a first week above $100m, of which only 6 have made >2.7x their first weeks. They are Jungle Book (2.79x), Wonder Woman (2.79x), Inception (2.92x), Avatar 2 (3.46x), Top Gun 2 (3.50x), and Avatar (5.47x)
So 300m seems tough, and would need to follow Wonder Woman/Inception trajectory for that. But I think $260m-$280m is very much in play. Same first week/DOM ratio as Oppenheimer would put it at $284m. Joker $268m.