>To help Amazon improve its products and services, I will use Amazon's publicly available products and services in the development and release of my Personal Game wherever possible
Does this mean you're not allowed to use Unity because Amazon Lumberyard / Open 3D Engine exists?
In theory if the two engines had feature parity it looks like that is the case. I suspect in practice it would look like you would at least have to provide some justification why it was not possible to use Open3D over Unity for your use case (perhaps some missing feature, however minor).
Does this mean you're not allowed to use Unity because Amazon Lumberyard / Open 3D Engine exists?