--generate-server set the options it needs that you left unset; to set them yourself, run (with the same input on stdin):
  datamodel-codegen --output models.py --input-file-type openapi --formatters builtin --disable-timestamp --generate-server fastapi --server-output server --server-package server --server-model-package models --openapi-scopes schemas api --target-python-version 3.11
