The one-liter mini-pc's are incredibly abundant & cheap on tbe used market. They mostly idle.under 10w.
I had some acer chromeboxes that were converted to linux, & those things idled at 5w! had em filled with 32gb ram. amazing little machines. the little i3 and celeron cpus were very weak but still held up well. had almost two years where i used one as my main desktop, literally velcroed to my monitor, but eventually decided the somewhat subpar perf (especially at 4k!) was a bit of a drag.
I bought a Lenovo M900 Tiny a few months back which is quite a few years old (think maybe 2017?) and upgraded it to 24GB RAM, 120 GB SSD and 500GB nvme.
With proxmox and a few vms running on there it idles around 11-12W which isn't raspberry pi levels of efficiency but still pretty decent.
I think the OP's server may have one or more mechanical HDDs in it that are consuming most of the power.
The author achieved some impressive savings, but I wonder how much lower it could go with a more efficient machine.
(Obviously that costs money and the article’s technique is free)