Missing categories-based JSON feed

If I’m understanding this help page about Feeds, there should automatically be a JSON feed for every category, but I’m not seeing that. I only get 404/Not Found responses.

In particular I want to use the feed https://marygrayson.net/categories/txt/feed.json (corresponding to Mary Grayson - txt).

Note that the corresponding XML feed is there and looks okay. But crossposts to Bluesky are missing included images, and I saw a reply on here somewhere that JSON feed worked better for that than XML. Feedback on that assertion is also welcome!

What theme do you use? You may have removed the alternativeoutputformats? Or possibly the json feed template.

This blog uses a “custom theme” based on “Marfa”. Any changes I made (long forgotten) would have been very simple & presentation/CSS-based, as that’s what “theme” means to me. Certainly I wouldn’t have done anything here with whatever alternativeoutputformats is.