The answer is simple: Jellyfin
I wish there was simply a way to make it show me the files I have available, for instance. There seems to be no way to do that. Instead, it insists on auto-detecting everything and then showing some preview image for that, along with some info scraped from the internet somewhere. It sounds nice, but instead when I want to watch "Space: 1999", it tells me I only have episodes of "Space Jam" or some other show I've never heard of. Or, it tells me I have no shows at all, but the shows are instead in the "Movies" section, or somewhere else entirely in the UI. It's bizarre.
I can see why a lot of people would get frustrated with it.
This is what I want most of the time too, so I love Kodi (media scanning/detection disabled. direct play from a share on my LAN).
We installed Jellyfin recently and noticed an option in Dashboard - Libraries -Display - "Display a folder view to show plain media folders". Haven't tested that fully yet.
Plex friends inform me it can't do a folders/files view at all :(
The Plex UI is better but only a little bit better. On the other hand they are really REALLY irritating with re-enabling their online adverts. Every time you upgrade its comes back again. Or your actual content ends up deep in a menu but the online nonsense is always there. Also you end up having to create a plex account to access your stuff and I don't know how much information they are tracking.
I just got tired of having to re-set it up all the time. Jellyfin seems much better so far, but its still early days for me.
I haven't had any trouble at all with the server side though (Linux).