There are a few threads around this topic. I have tried them with no success. I have a direct install of HA (115.6) on a RPi 3B. I have added HACS and Feedparser to get a custom news feed.
This has been successful and I can see my news feed using the Glance Card. However I am not able to get any custom card to work! I have tried installing a custom card (any card) via HACS frontend repositories. I can add the repository to HACS. I can download the raw json module and add that to the correct folder that I create under in the config/www/ folder.
But on adding the url and type to the raw editor on the overview page I never see the Card. If I use the browser inspect function I can see the json files are there. But they have an error message - unable to fetch resource. I can still be making some mistake although I have tried this several times (and also via creating the ui-lovelace.yaml). An ideas on what I am doing wrong or missing greatly appreciated.