Pure Arch isn't going to give you what you want. EndeavourOS is probably a better option. Nice installer, a relatively kind and helpful community on their forums, and you can use the Arch wiki to fill in the gaps.

https://endeavouros.com/

Per their website, everything in the Pixel line apart from the 10a is supported. They will be supported as long as firmware and security patches are available. https://grapheneos.org/faq#supported-devices

Mine works on PopOS which is also Debian/Ubuntu like Mint. There are some instructions here that may help. https://www.8bitdo.com/steam/#pro2-popup

Lots of x86 machines are hitting the curb this week because they won't run Windows 10. One of those with a Linux distro installed will do what you want. Follow the directions in Jellyfin's documentation and you should be good. Adding your devices to a Tailscale network is the fastest way to be able to access your content outside of your home network. FireTV has a Jellyfin client and can also be added to Tailscale.

Last I checked, Roku doesn't have a Tailscale app. So unless Tailscale is working on your router the TV can't see the desktop's Tailscale IP.

I have a similar setup, and Roku only works if I connect to Jellyfin with the LAN IP. If your desktop isn't on the same LAN -- wifi or ethernet -- it won't work.