Is a NAS still considered underpowered to run Roon Server in 2021?
A mid-range NAS like the Synology DS720+ will have a modern Intel 64-bit processor. For instance, the Celeron J4125 has similar performance (single-thread and multi-thread) to that of a 5th generation i3 processor in a NUC.
I currently have a DS-920+. It can do PEQ on native DSD64 without breaking a sweat.
I am adding another Roon Server. I can get a NAS (DS-720+) or a NUC (8i3). They cost roughly the same. The NAS can be used to backup files. The NUC can do more processing, which I may or may not need.