Hi, the generic aarch64 image was initially released as a container image only to be used in containerised applications. As such it does not have raw images to download.
We are working on releasing an updated image suitable to use in physical ARM server hardware. We have an open issue tracking this work in Release generic-aarch64 to production with only automated tests · Issue #84 · balena-os/balena-generic · GitHub which you can follow. We will also update this ticket once the issue is closed.