You can also use the Halium (11, because of device’s vndk version) as a porting base and structure the port in a similar way to Fxtec Pro1-X and Volla 22 ports by @piggz.
I’ve been working on getting FP5 kernel compiled for Ubuntu Touch, and that part should be mostly reusable for SailfishOS: UBports / Porting / Community Ports / android11 / Fairphone 5 / fairphone-fp5 · GitLab