Uhm Jellyfin Media Player on a computer ? if yes, you can use KDE Connect on your phone and computer. it's an awesome tool!
Jellyfin: The Free Software Media System
Current stable release: 10.10.3
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I've been using Unified Remote to control my media PC (including any applications on it, such as Jellyfin) from my Android phone. I just use the track-pad remote, the keyboard input for typing, and the volume rocker for volume control. Though, there are lots of specialized remotes, including media remotes, available.
This has worked well on my media PC running Windows. However, I'm about to rebuild and I'd like to run Linux instead. In the past I've had trouble with Unified Remote on Linux; the text I type, especially when pasting, comes out as gibberish. As such I've been looking for an alternative and will probably give KDE Connect a try.
Yatse does that. It has more bells and whistles if you pay for premium or whatever it's called, but if you don't venture outside the first screens, it can be customised into a great very basic remote.
Can Yatse be used to control Jellyfin Media Player?
I only use it to control my Kodi clients with the Jellyfin plugin but it does that wonderfully.
I was wrong, I'm afraid. It turns out that yatse can access the jellyfin server, but jellyfin needs a player, not a remote control. Yatse can do that, but it's not a remote control. Sorry!