It is stored in
It is saved as a new name, copying the Joomla! override structure that I copied after clicking into my template in the back end and then clicking "create override" on the override I wanted. This showed me the naming convention.
I can see the override if I go into Articles > Category in the backend and I can select the new override.
So I have 3 files.
The files have not changed from the core files at the moment.
At some point I could go into Menu > Main Menu > My Category List Menu Item
Then I choose options, and I could see my menu override there.
I can't see it any more and I can't understand why it disappeared.
I have also created a
default-filedownload.xml file as I'm aware that can help. My override can be seen if I put these 4 files into /components
/com_content/views/category/tmpl/ then I can create a new menu item.
I don't want a new menu item
How can I make something appear in a menu item, under options, where it allows me to choose a layout.