Run Jellyfin instead. I don’t know how Plex has stayed as popular as it has.
Easy, Plex can pass the spouse test. Jellyfin has yet to pass the spouse test…it’s getting there though
I tried Jellyfin and the performance for me was sooo much worse than Plex on the same system. Videos took forever to play. Also Plex is way easier for me to share with family than Jellyfin.
You can check to see if you can enable hardware transcoding. I find the delay is usually transcoding building up a buffer and if you have a good GPU/APU in your server it’s often a lot quicker.
Pretty sure on jellyfin by default that is off. Mainly because you need to install some packages to get the devices available under linux usually.
If you were playing videos with subtitles on android, you might have run into the slow subtitle burn in bug.