My first NAS was an old desktop that I got for $300 running an FX-6300 and a GTX 550, I slapped a couple hard drives in there, installed Ubuntu, and made an SMB share.
I’d recommend installing TrueNAS Scale on a system rather than doing what I did in part due to it being so much better than what I was doing, but you could run it on a potato if you wanted.
Hell my latest NAS upgrade is going from a PowerEdge T610 (tower server from like 2010ish) running TrueNAS Scale to a normal desktop (from 2017) running TrueNAS Scale
If anything using normal desktop hardware makes servicing it easier than using old server hardware