The missing piece for me was understanding a layout was needed and where to put it.
(I found various examples of ranging and I was somehow trying to get it to work by making a shortcode that would put in html into my _index.md)
Update: I got it to look just the way I wanted.
From what you taught me, and the links you pointed me to, I figured I could reuse my theme’s list layout for my custom list too.
So I used that as my layouts/_default/blogs-tagged-other-projects.html and dropped your range code, in there.