Issue with index.html

I am noob when it comes to this stuff so bare with me, but I am running Jellyfin 10.11.8 via compose and am trying to install the plugin Jellyfin Roulette. The issue is that this plugin works by modifying the index.html and cannot run because it does not have the permissions to modify index.html. But my understand is that this doesn't exist any more and is not how Jellyfin serves its web interface? If so, does that mean all plugins that modify index.html no longer work, or are they installed in a different way, or am I just completely wrong about all of this? It does say on their GitHub that it works on 10.11 so I believe I am just misunderstanding something.