Currently it seems like the only os/arch combo the docker image being built is linux/amd64.

For our case, it would be a cost-saving initiative to have an ARM image, to be able to utilise the more cost effective (and for the next 12 months, essentially free) t4g instances in AWS (currently running nicely and happily, 24x7 on t2.small)

Reference - https://aws.amazon.com/ec2/faqs/#t4g-instances

I'm not familiar (yet) with buildpack configuration, so I won't be able to submit a PR myself as of this time.