These are created using Jim Neilson’s reboot of the original Readlists tool from Readability: https://readlists.jim-nielsen.com/
Kindles do not support epub, so you must take the epub you get from Readlists and convert it to mobi with Calibre.
For a future project of extending the Readlists tool, this npm package could be helpful: https://github.com/moszeed/kindle-periodical
You can open the mobi URL in the experimental browser on your Kindle to download it. You can upload the json file that you can import into Readlists to make changes and additions.