I have tried everything mentioned on web sites to install HACS - without success.
My feeling is that HA is not recognising the config/custom_components directory (under which hacs resides). Can anyone suggest a simple component to install which uses this config subdirectory so that I can verify that at least the directory structure is being addressed correctly?
Anniversaries is a pretty simple custom integration, just follow the manual installation steps, restart HA, then you should be able to configure a sensor through the Integration setting page.