I don't even understand what kind of webui one would want.
All you really need is a bunch of disk and an operating system with an ssh server. Even the likes of samba and nfs aren't even useful anymore.
File history, sharing and user management are some of the common ones I can think of.
A bunch of out-of-the-box NAS manufacturers provide a web-based OS-like shell with file managers, document editors, as well as an "app store" for containers and services.
I see the traditional "RAID with a SMB share" NAS devices less and less in stores.
If only storage target mode[1] had some form of authentication, it'd make setting up a barebones NAS an absolute breeze.
[1]: https://www.freedesktop.org/software/systemd/man/257/systemd...