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