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Getting .net runtime 404 errors trying to install Jellyfin Server
(sh.itjust.works)
The beloved lightweight distro
You didn't upgrade before installing. -y updates the package list to match the mirror, -u updates your system (and you should not use them separately, so if in doubt always use -yu).
So when you try to install (without synchronising the package list first) your system looks at it's outdated package list, then requests files that are no longer on the mirror as they are already on a higher version.