There's a demo on their official website: https://demo.jellyfin.org/stable/web/index.html
I'm posting this pretty late, so doubt many will read this, but I just want to make a point that the attitude of "I don't need a screenshot, there is a demo 3 clicks away behind a username and password that is murky to find the details" is a terrible message to send.
When you don't bother to put a screenshot of an app as large and as beautiful as jellyfish, for me, it screams, "this is NOT going to beworth your while to install. If you have the knowledge, fine, otherwise, there's a great barrier to entry here. Just to see it, it's 3 clicks and some keystrokes away, imagine what installing and running is like."
The screenshot on the other hand would say to the user, "here is this beautiful app. Now decide if it's worth it to check out the demo and maybe read a few of the docs."
Edit I don't care about cookies extension removed it. So username is demo. There's no password.
#disclaimer,.disclaimer{display:none !important}
I am not sure how wise it is to hide all elements with ID or class "disclaimer", to be honest. There are other rules that seem like a bad idea as well (same thing for 'notification', 'notifications', 'notice', 'notices', 'alert', 'overlay', 'modal'...).