SC on Windows / Linux / MacOS

The official Jellyfin Desktop client or the Jellyfin MPV Shim client.
Note: The Jellyfin Desktop client is going through a complete re-write, with currently no 'stable-release' yet (although, the current release is sufficient).

Old versions: https://github.com/jellyfin-archive/jellyfin-desktop-qt
New versions: https://github.com/jellyfin/jellyfin-desktop

For the 'New version', open up that link above and find the right client based on your computer. Click on the link that matches your computer system. You would see a .zip file that you may have to extract in order for you to get the executable file / installer / .dmg (MacOS) / .exe (Windows) / .AppImage (Linux) / .flatpak (Linux) etc.

Extract the zip file, install, open the app, enter SC's address, enter login details and you're done!

The differences between the Old versions and New versions?
The Old versions are Qt-based, and the New versions are CEF-based.
Both versions still uses LibMPV as the media player client, which is why it can play all the video formats you throw at it with ease.

The other option is:

Jellyfin MPV Shim client - which can be obtain from here:
https://github.com/jellyfin/jellyfin-mpv-shim/blob/master/README.md

Jellyfin MPV Shim client lets you "cast" Jellyfin media instance(s) to your system of choice, acting as a cast device. It then plays any media through MPV player on your system. This gives you a more direct approach when playing any media on SC, as well as satisfaction without having to really install anything (if you opt for the portable version).