I use Plex because I already have it in use, though only on mobile/Windows. With real computers, I just mount the music volume and use mpd. Both work pretty well through a VPN too.
depending on your NAS, you might be able to run [0] Logitech Media Server; I still have it running on mine, and use it occasionally - I use it particularly for "play random album" which I have never seen elsewhere, and is great if you have a large collection of ripped music.
I keep things simple on the serving side and just choose an appropriate client. I just use a NFS share on a Raspberry Pi with attached SSD to make FLAC files available on the network.
Playback is with Volumio on a Raspberry Pi that I have connected to the Hifi, Audivana on my Mac, and the nPlayer app on any iOS/Android devices. nPlayer is really great for video too.
I run Navidrome [1] in a Docker container on my Synology NAS.
It’s lightweight, can handle huge music collections, has a good web interface, supports Last.fm scrobbling, transcoding from the most formats and AirSonic-API for use with a wide variety of players/apps.
I run both Plex and Roon on my Synology NAS. The former is used for videos/photos and to share with the in-laws, while the latter is mostly for my own owned & streamed music. Roon's not cheap, but it works for my various use cases for it.