In case you have a fritz!box router, take a look at fritz!app fon and see if that is what you want.

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I planned to use nfs, since it is one of the options of TrueNAS and it works on both windows and linux.

It will be used just for file storage. But what exactly do you mean by “lighter hardware”? april said anything more than a raspi, so better than the quad-core Arm Cortex A76 processor @ 2.4GHz from the raspi 5? (ik that truenas is for x86 and not arm)