Both Macs are on the latest Big Sur build.
There is a recent project on Apple’s part (https://github.com/apple/tensorflow_macos) to make TensorFlow run on CoreML and thus take advantage of both CPU and GPU without needing CUDA or OpenCL. I think this fork has actually been merged into the main TensorFlow branch.
I actually managed to get NengoDL to run on Apple Silicon, but it is not working properly yet.