If you don’t mind plugging stuff in yourself, literally any quadcore x86 CPU with integrated graphics after 2016 will run jellyfin just fine. Then you can load up on SSDs as you see fit.

Any prebiilt NAS you can find with anything within the last 8 years in the CPU will also be just fine.

idk what resolution you use for streaming but my raspberry pi 4B runs plex at 1080p just fine as long as it isnt using x265/AV1 (but on jellyfin you might be able to use the Pi’s GPU for transcoding).

I use nextcloud too but it’s a tiny bit slower than I’d like, but that’s likely a wifi issue i think.