Using doxygen version 1.9.4 (5d15657a55555e6181a7830a5c723af75e7577e2), Doxygen XML is generated and passed into Breathe to be rendered with Sphinx. If any C# enums are present in the input, Breathe's Sphinx renderer throws an exception:

Exception occurred:
    File "C:\Users\MyUsername\company\repo\build64\venv\lib\site-packages\breathe\renderer\sphinxrenderer.py", line 
  332, in create
      cls, name = DomainDirectiveFactory.cs_classes[args[0]]
  KeyError: 'enum-class'

(Full traceback is here).

An example input that causes the error is here.