I don't know that but I clearly know one thing
Time for the ultimate Mihawk tard theory.
Mihawk wasn't included in the RED movie because he is actually stronger/more capable than Shanks and Oda would have to showcase Mihawk's full moveset and hype but he doesn't want it because it must be a special moment like Mihawk vs Shiryu or his final duel with Zoro.
Simply. Shanks' supposed movie was not worth Mihawk hype
Quietly disappears into the shadows and cries in the corner