Our website runs on a linux server, can you not use it though

Damn thats a cheap watch, is it Chinese too?

Whats your setup? I just Ngnix Proxy Manager, Jellyfin etc in Docker. Modify ufw rules and also install this on the server (linux) https://github.com/friendly-bits/geoip-shell

Id switch to mint, most windows like and all the knowledge youve learned will work on it. If you want true stability go Debian.

Jellyfin is avaliable on almost everything as far as I am aware (excluding games consoles). Havent used Plex much but I know for Jellyfin the majority of my users issues relate to iOS. Id check your encoding of the specific file they have issue with M series macs can be weird with certain encodes of h.264 for example or a specific audio type. Here is a decent breakdown of codec support by client/browser https://jellyfin.org/docs/general/clients/codec-support/