For years I just wanted a good user experience playing video files from my MBP to a TV, I spent a lot of money (on NAS, chromecasts etc), used a lot of software with objectively terrible user experiences (Plex I'm looking firmly at you). Finally, I discovered the combination of Jellyfin and Infuse App. It works really well.
I’d be interested to know what you find terrible about the PLEX UX. I’ve been a happy user for years and have found the user interface to be reasonably intuitive. Perhaps dense in places, but certainly not terrible in my opinion.
I can watch my Jellyfin shows from a Flatpak local client on my desktop, pause and move to my phone, pause and move to my TV. That's three different operating systems, and at no point do they transcode, because it's not going through a browser.