Jellyfin is open sourced and supported by donations. I’ve used it for around a year and I can confirm there have been no fees, tracking, or anything else.

FOSS, donations

It’s a FOSS application. Software that users deploy on their own hardware to host videos that they store themselves and make them available for clients to view either on LAN or the internet. It’s not something like a Youtube alternative that would need to pay hosting costs for petabytes of (pirated) media, the only costs Jellyfin’s developers incur are the costs of labor (coding, graphic design, debugging, etc)