At this point, I’d say build your own if you are wanting anything more than basic file sharing.

Lots of resources out there and even NAS style cases to make it basically the same as any off the shelf NAS.

Xenology has been mentioned here, but I haven’t used it

FreeNAS is good, but I haven’t used it in years.

OpenMediaVault is supposed to be good, but again I haven’t used it.

Unraid is good and has super easy support for docker. I primarily use this because of its ability to use different disk sizes for the array and does what is the equivalent of software RAID. It’s not the fastest thing on the market, but for my use case (primarily Plex/Jellyfin) I don’t need the fastest reads or writes. It supports hardware passthrough for VMs or to docker containers so they can take advantage of hardware for acceleration. It also runs off a flash stick, so I don’t waste any disks on the OS.