I’m a huge supporter of open source, so Plex being closed alone makes it gross to me. Very little about Plex felt selfhosted.
I also like to tinker a lot and jellyfin lets me screw around with much more under the hood - precise encoding settings, dlna customizations, I’m sure there’s more but the primary driver was ideology. I’m not giving my money to some company that’s primarily developing features I don’t want so that I can use my own media to the fullest.
I’ve had very little issue with hardware accelerated encoding, but I already had the right drivers installed and on unix OSes that’s probably the hardest part