That is really cool! I made something similar, but it's not as feature-rich as your version.

https://medium.com/gitconnected/i-created-an-automated-medium-newsletter-here-is-how-you-can-do-it-f2611f4fb9b1

My code collects articles from my Medium RSS feed regularly and once a month I put them in an email, and send them to my subscribers with the Sendinblue API. There are also placeholders included for sponsors or affiliate links, but as of now, I need to edit them manually if I want to change them. Nice to see what my ultimate goal can be. Thank you for your article!