Low-end NASes have been using ARM for a long time.
The higher end x86 NASes are advertised closer to "home datacentre in a box" solutions that offer VM/container runtimes and third party software markets.
So far, x86 is significantly more user friendly and performant for these use cases: the "desktop-ish performance for desktop-ish prices" range doesn't really have many hardware options (Apple certainly won't sell theirs to OEMs, and the Snapdragon 8c is a bit on the low end, and the real data centre ARM many-core monsters are too big); and the software offerings aren't quite as user friendly either.
The higher end x86 NASes are advertised closer to "home datacentre in a box" solutions that offer VM/container runtimes and third party software markets.
So far, x86 is significantly more user friendly and performant for these use cases: the "desktop-ish performance for desktop-ish prices" range doesn't really have many hardware options (Apple certainly won't sell theirs to OEMs, and the Snapdragon 8c is a bit on the low end, and the real data centre ARM many-core monsters are too big); and the software offerings aren't quite as user friendly either.