It's a perennial thing with Jellyfin that it doesn't have the app / remote access support Plex provides. By itself it's a fully functional network media server, but by design it doesn't have the ability to reverse tunnel and it doesn't have the corporate infrastructure that gets it's app onto devices.
Yes you can set up wireguard / VPN access. Yes there are workarounds that can get Jellyfin streaming to most devices.
None of that matters when trying to talk someone on the phone through connecting to your server through the internet.
Plex is an account, it looks like a streaming service, it requires zero knowledge. I'm fairly certain some of my relatives have no idea it's streaming from a server in my basement. Jellyfin they have to trust you enough to setup separate other apps / configuration and have the patience / attention span / ability to follow directions to do so.
The ISS has a lot of big solar panels. The other big panels they have are thermal radiators.
They have to have quite large thermal radiators because it's very inefficient. The ISS has people and a very small amount of computing power.
Data centers generate several orders of magnitude more heat. You would need several orders of magnitude more thermal radiators than you would solar panels. The bigger you make the data center, which is important for density since you're introducing a lot of lag due to the speed of light, the less room you have to put thermal radiators or solar panels.
Then you need to work out how to get spare servers, and/or server parts up and down from the Data Center. All of these things are consumables, and all of them have significantly more wear and tear outside of the Earth's atmosphere.
It is possible. It is not efficient or sensible. It sounds cool, it doesn't require buying land, and there aren't currently international agreements about doing dumb stuff in space in the same way there are for doing dumb stuff in the ocean.