I have recently been trying to use the standard network installer for
Chimaera (netinst, 4.0) in an automated installation with the kernel
parameters

      auto=true url=https://server.example.com

There is an error in the installer which causes the path for the
preseed.cfg file to be miscalculated as

      http://server.example.com/d-i/bullseye/./preseed.cfg

rather than the documented

      http://server.example.com/d-i/chimaera/./preseed.cfg

Fortunately, adding a symlink in the web document tree (or a URL
rewrite in the reques processing) works around the problem.

Best wishes

     John Hallam