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.
Power isn’t from drives, if your OS spins them down (as any NAS solution should).
See my other comment.
You can only spin drives down if they’re idle. If you have a service that touches it - say, homeassistant logging data, tvheadend updating EPG - then they’re going to keep spinning.
I would hope one would use an SSD for something like HomeAssistant. HDDs really shine as bulk media storage (music, pictures, video) not as storage for what would be the equivalent of running an OS on it.