The author explains how to turn an HP t520 Thin Client, purchased for $25, into a Time Machine backup appliance for MacOS. They wanted a low-power and small option, and the t520, which consumes 6W at idle and 10W otherwise, was a good choice. The internal storage is limited to 64GB, but an external USB3 drive can also be used, with the benefit of easily disconnecting a drive and putting it into secure storage or attaching it to a different PC. The author also details the installation of Bodhi Linux and necessary packages for Time Machine operation, along with tips for accelerating Time Machine backups.
https://tomverbeure.github.io/2023/06/25/ThinMachine-a-Thin-Client-MacOS-Time-Machine-Appliance.html