This is designed to work with an existing Jellyfin server, so you should be able to even install and use this alongside any existing Jellyfin mobile apps you have installed.
It lists the following additional features:
🚀 Skip intro / credits support
🖼️ Trickplay images: The new golden standard for chapter previews when seeking.
📺 Picture in Picture (iPhone only): Watch movies in PiP mode on your iPhone.
🔊 Background audio: Stream music in the background, even when locking the phone.
📥 Download media (Experimental): Save your media locally and watch it offline.
📡 Chromecast (Experimental): Cast your media to any Chromecast-enabled device.
It has been updated as recently as a week ago, so looks actively maintained by 10 different contributors. It is available for iOS and Android.