That’s all a NAS has ever been, just a PC that specializes in storage. “NAS” isn’t a specific product, either - it’s whatever hardware you set up to function as such. My own NAS is a 2014 Mac mini running OMV (Debian 12 based) with a 4-bay locking drive dock attached to it. Works great.

I took images of my gaming PC drives (500GB, 2TB) onto a 4TB spinner, then shoved that spinner into my NAS’s dock. With 2 minutes of point and click configuration, I can access those images from my gaming PC’s new Linux install over the network to copy whatever data I might need. Easy peasy. No Synology needed for that.