I like focusing on stuff I can buy now as opposed focusing on stuff I might buy in the future, if various motherboard manufacturers get around to actually offering motherboards with said chip sockets.
The AM4 socket is plenty performant, ditto the chip universe one can choose from. Even very low power configs are possible with the -G sub variants available on eBay vs. the more common -x types that aren’t apparently as good at throttling themselves. The -GE version has a slightly slower base clock (3.4 vs. 3.9GHz) but the turbo clock is the same (4.4GHz), ditto cores/cache/etc and the TDP of the 5650GE is only 35W vs. 65W. For a small NAS, the GE version likely makes more sense, especially since 3.4GHz is plenty fast for a small file server.
From a rust file server POV, SM has pretty much abandoned the mini-itx form factor with the exception of the atom board. Also note the clever use of Oculink by gigabyte for their mini-ITX board - i.e. how to expose a lot of lanes for SATA OR NVME flash applications despite working within the constraints of mini-ITX. SM could have done that also with it’s D-series or Ryzen offerings but chose not to.