I am using a cheap custom setup with a Ryzen 3600 and 16 GB of ram with TrueNas and works ok. Jellyfin takes a few seconds to get started but runs fine otherwise. I can even run 4k streams but only works smoothly if i encode them with the fast decode option. This was very cheap because of the old hardware, about $300 before the drives.

The only thing I would change is to get a CPU with integrated graphics. Some can help with decoding and massively simplifies the first time setup.