I have an ancient Qnap NAS (2015) which is on borrowed time and I’m trying to figure out what to replace it with. Keep going back and forth between rolling my own with a Jonsbo case vs. a prebuilt like the new Ubiquti boxes. This is an attractive third option of a modest compute box (raspy, NUC, etc.) paired with a JBOD over USB. Can you still use something like TrueNAS with a setup like that?
If you don't mind using m.2 drives, check out Beelink ME Mini. The m.2 drives are going to be limited by the PCIe 3.0 x1 bus [1], but you get a very neat and small appliance-like box that can handle home storage workloads really well. Just keep in mind that you'll need an additional OS drive: TrueNAS will probably wear that eMMC out in a matter of a year or two.
[0] https://www.bee-link.com/products/beelink-me-mini-n150
[1] https://youtu.be/TkFfTekB3eM?t=1034
Local storage should be like a home appliance, not something we build even though we can.
When things inevitably need attention it’s not about diy.