As iDownloadBlog reported a few days ago, the new Apple Silicon-powered M1 Macs do not support external GPUs (eGPU), but that could be a temporary hiccup. That's because macOS Big Sur has bee discovered to detect a connected eGPU over Thunderbolt 3, although it's not exposed to the user or actually accessible for compute and graphics tasks.
Lack of eGPU support in M1 Macs may only be temporary