A:Answer Yes it will be. During the conference as well as their blog here https://blog.playstation.com/2020/09/16/see-the-marvels-spider-man-miles-morales-new-gameplay-demo/
says that Miles Morales will be launched on both PS4 and PS5. Here is their exact words, "We’re also excited today to reveal that Marvel’s Spider-Man: Miles Morales will be arriving on both PS5 and PS4. Yes, that’s right, we know that some of you may transition to PS5 at different times, which it was why it was important to us to release the latest title in the Marvel’s Spider-Man universe on both consoles. "