I run Jellyfin on a RPi 4. It works for me, but only because I use codecs (h264/265 for video, AAC for audio) that are definitely supported on my players (NVidia Shield TV and android phones). This leads to Jellyfin not touching the files and just providing them to the player. As soon as any codec doesn’t fit my client (for example OPUS audio) Jellyfin starts re-encoding the audio and remixing the stream and the stream just fails.

So yes: RPi4 is generally not able to run Jellyfin unless you have a very specific setup.