If you’re getting downvoted it’s probably because you sound a bit condescending.
Anyway, most of your issues are Ubuntu issues, not Linux issues. And as you may have learned, most Linux users don’t really go with Ubuntu anymore as a recommendation. Personally, I use Fedora with as many flatpaks as possible and have a great experience.
Clicking on a deb (or .rpm) to install something is a last resort imo. Install from the package manager first, flatpak or snap next.
Variable refresh rates aren’t something I care about so I don’t know 🤷🏻♂️ but sounds very firmware/hardware dependent. HDR is just not implemented fully yet, but being heavily worked on. Linux is in the middle of the final push to switch X to Wayland which will likely fix these kinds of issues once fully adopted.
The nice thing about Jellyfin is that you can point Jellyfin and Plex to the same media folders and both will work, to try it out.
I would get a Synology with intel Quicksync if you go the Synology route for hardware transcoding. Unfortunately, a lot of the new models don’t have it.
I just have a 220+ but would maybe get a 4 bay model if I did it again.
Glad I already migrated to using KeepassXC on the desktop for TOTP codes, partially out of frustration trying to use the Authy Linux desktop client.
And hey, now I own my data!