Thanks! I used Pixelmator Pro to put the images together. I just made one long image that I cropped at the end into the screenshots you see on the App Store. For the iPhone templates, I think I exported a template from Sketch, but I later found out that Pixelmator also has them (you can find them under the Mockups category in the New dialog).
EDIT: Oh, I just realized you might be referring to my blog, in which case I _can_ take credit for that :P. Thanks again!
[1]: https://www.chakra-ui.com/