Why do you need a bunch of SATA ports? Just get a cheap SAS2 PCIe card on eBay.
There are definitely low power ARM boards with a PCIe lanes. Typically its NVMe, but you can adapt that to 4x PCIe 3.0 which is a lot of bandwidth for HDDs. Not sure why you need a lot of memory for a NAS though, but they do have boards that have 32GB of memory.
What's wrong with this?
https://www.amazon.com/Radxa-5B-Connector-Computer-32GB/dp/B...
And connect a card like this to the NVMe PCIe which you can connect 8 SATA HDDs to with SATA breakout cables.
https://www.ebay.com/itm/155007176276
If you need more than 8 HDDs you can get a SAS2 expander to connect to the SAS2 card and then you could easily connect 24 HDDs with a 6 port SAS2 expander and breakout cables.
Or if you put this small board and card into a server case that has a SAS2 backplane with expander built in, then you can just connect all the disks that way.
Another option, not ARM, but still low power and neat.
https://www.lattepanda.com/lattepanda-sigma
This has Thunderbolt 4 which you can connect to a PCIe slot like this:
https://www.dfrobot.com/product-2832.html
They have a lot of neat stuff, you can get the tiny LattePanda Mu, and dock it in this:
https://www.lattepanda.com/lattepanda-mu
https://www.dfrobot.com/product-2822.html