Making a Linux home server sleep on idle and wake on demand (2023)

Most of the time you don't need data center sized home servers even if you do test data center sized software solutions on them.

So instead of the Pi solution, how about using a server that idles at 10-20 W?

This. My Lenovo ThinkStation with a Core Ultra 7 265K idles out at ~10W headless (measured with a smart plug), while it can be very fast when needed.