I use a 3rd party client called Wholphin and it works great.

Also it helps to set up profiles in sonarr/radarr to make sure you're getting media thats compatible with the devices that will interact with Jellyfin, and filter out formats that cause problems. I use Profilarr to load in community made quality profiles to sonarr/radarr and then i copy them and tweak them for myself.

Before i started doing this i had loads of problems with Jellyfin not being able to play stuff, and now everything runs perfectly.

The biggest discovery I made that was causing a lot of my problems was HDR formats. HDR10+ only really works on Samsung TVs for example. I dont have a Samsung TV, so anything I had that would try to play that content would come out a weird green/purple colour. Content with Dolby Vision Profile 5 would flat out not play on devices that don't support Dolby Vision. Dolby Vision Profile 7 falls back to regular HDR10 when the device doesnt accept DV, so that works, but DV Profile 5 doesnt do that.

I was able to filter out HDR10+ and DV Profile 5 using quality profiles and all my playback issues disappeared immediately.