Although there have been no official announcement about Chainsaw Man trailer being pre-animated but according to an article by Otaquest, there is a possibility that Studio Mappa is pulling the same trailer trick for Chainsaw Man as they did for Attack on Titan final season trailer.
Chainsaw Man trailer was released during the Mappa Stage – 10th anniversary. Trailer has gotten more than 12 million views on Youtube and Twitter combined.
According to Otaquest, the kind of footage that has been used for trailer infers that the trailer is pre-animated. If the shots were taken from the actual production, for example, then the scene featuring Aki, Denji, and Power eating at the dinner table should not have even been animated yet. Unless the production is several episodes and even seasons ahead, which is highly unlikely given how many projects Studio Mappa is working on
Furthermore, some of the shots in this first Chainsaw Man trailer are entirely new, such as Kobeni playing in the ocean with Power and Denji. Undoubtedly, they are meant fpr manga-reading audience only.
This is not the first time Mappa has used pre-animated footage for trailers. Previously, Attack on Titan trailer by Mappa was pre-animated. After couple of days of releasing the Attack on Titan trailer, Mappa did clarify that the trailer was pre-animated but it was too late because the damage was done.
Furthermore, a popular animator leaving the Mappa studio due to poor work conditions does not paint a good picture of work ethics of studio Mappa. Production quality of Chainsaw Man will depend on how much time they take before releasing it. Keep in mind that Jujutsu Kaisen animation looks that good because Mappa Studio took their sweet time before relasing the final product.