A Raspberry Pi will work as a Jellyfin server, but it will really struggle if it has to transcode any media.
If you want your Jellyfin server to be up and accessible at all times, I would suggest getting a second hand PC. I’m personally a fan of small form factor mini PCs. Anything with a 7th gen Intel processor or newer, with integrated graphics, will be able to hardware transcode anything but AV1.