Many dedicated NAS devices can handle hardware transcoding and provide solid functionality for Plex when used as the PMS. Synology and QNAP are common prebuilt devices with good Plex support (I use Synology). This article is particularly helpful: https://support.plex.tv/articles/201373803-nas-compatibility-list/
NAS devices can do LOTS of stuff and are designed to be up and running non-stop so I personally prefer NAS based PMS over desktop but it all depends on what else you’re getting a NAS for outside of network based storage of course.
Here’s a pretty big thread about using M1 based Mac for PMS: Plex Media Server running on Apple Silicon M1 chipset i.e. new Mac mini, MacBook, etc - #17 by Balthazar2k4
