I have been using an old PC as NAS and running docker containers (Immich, Nextcloud, paperless-ngx etc.). I got 5 3.5" HDD disks and a Nvme. Even on idle, I am consuming 50-60w. A friend of mine is selling a Qnap NAS which is a dedicated machine and probably consumes less power, although I don’t know if it’s worth it.
You’ll want to look up the QNAP as well. I’ve seen reports with quite some variety on the power consumption. Depending on the exact model, it could be somewhere in the range from 25W to 55W… So could be less, could be the same. And have a look at the amount of RAM if you want to run services on it.
Ram is definitely abysmal on Qnap, so it’s one reason for hesitation. But I wanted to get some idea how much power saving is possible on dedicated NAS. If it’s not much, I would rather keep my PC.