There's a Jellyfin app for webos, but the garbage store does not really let them to publish/update it. You can get an up to date version from the store app called Homebrew Channel.

This store app can also handle rooting related things, but that's not needed for Jellyfin, and both can be installed on a nonrooted TV.
That's an other question that the TV will regularly delete these apps until you root it.. but take it as an "evaluation period" haha, if you like the app there are a few ways to make the app persistent.