I personally use jellyfin and it works well enough for me to watch my movies and shows. I don’t use the app but just use the browser but there are plugins for kodi and various apps too.

Ive not used Plex myself and from what I have read it does the job too. A few friends use it and are happy. I read recently they let go of 20% of their staff.

For me it comes down to it like this: do I want a company to have control over my viewing experience with closed source software or do I want a community FOSS experience under my control. That is very important to me but it depends on your own needs.

https://www.rapidseedbox.com/blog/jellyfin-vs-plex