Only accessing jellyfin via android app is without issues

[TheDreadPirate]

Oof. That 3-4w CPU was underpowered when it was new. When it is just audio transcoding, it is making that conversion at about 60-70FPS. Perfectly fine if it was the only stream happening. You could probably get away with 2 audio only transcodes.

The problem is when you are video transcoding. It looks like it is video transcoding due to the PGS subs needing to be burned in. That transcode is happening at 16-20FPS for a 24FPS video. As you can imagine, transcoding at less than real-time is not good. The output for both of these video transcodes was 1080P.

720P for transcodes is pretty much a necessity for your setup.