Installed packages are not found

[viraptor]

I'm getting the an error when trying to use OmniSharp, where it doesn't find any of the installed packages:

:: [17:56:32.218] <-  OmniSharp textDocument/publishDiagnostics: {...
  {'range': {'start': {'line': 0, 'character': 6}, 'end': {'line': 0, 'character': 13}},
  'severity': 1, 'code': 'CS0246', 'source': 'csharp',
  'message': "The type or namespace name 'Spectre' could not be found (are you missing a using directive or an assembly reference?)",
  'tags': []
 },...]}

This happens for any package at all. I'm running macos 14.5 (23F79) with only .net 8 sdk installed. There's no more related information in the logs, so I'm not sure how to debug it further.