Apple Silicon M1 Mac detection of Thunderbolt 3 eGPU gives hope for future support | AppleInsider
The lack of support for external GPUs in Apple Silicon M1 Macs may only be temporary, as a connected eGPU is still detected, but doesn’t do anything.

Apple Silicon M1 detects a Thunderbolt 3 eGPU enclosure and any Thunderbolt monitors daisy-chained from the Thunderbolt 3 eGPU enclosure; however, the GPU in the Thunderbolt 3 eGPU enclosure does not function correctly to display anything on any tested monitors.

Hope remains for updated drivers allowing eGPU expansion of the Apple Silicon M1.