Premieres Fall 2024. There is also a PV you can check out here. I can’t find an English language synopsis yet, but here is a slightly edited MTL I got from the Japanese source:

Fureru is a story about three childhood friends who are connected by a mysterious creature. Set in Tokyo, the film depicts the true connection between the three after becoming young men, and the people around them.

Other info is that it is being made by Cloverworks with many of the same key staff as Anohana.

Edit: English article has since been published for more info.

Edit 2: Another English article with a bit of a synopsis:

Fureru is being described as a coming-of-age film set in present-day Tokyo, centering on childhood friends who find a creature with mysterious powers that pushes them to discover the bonds that tie the three students together.