The theme has a section on usage, and if you need a theme to test, we also have a directory of those. The benefit of this set up is you can follow the instructions for a theme with that content repo, and then compare it to the demo page for any given theme, and see how they compare (presumably they will be similar!).
I don’t use Jekyll, so I’m reaching here: in the Hugo support forums we need code to troubleshoot. Sometimes we don’t, but 90% we do, and anything else is just guessing. There is no Hugo internals that is causing your issue, it’s templates all the way down.
I thought we could knock this out, but I’m out of energy. My suggestion is to create a test project in a public repo and try things out there so you can easily point out what you are doing when seeking assistance.