Github Pages theme not appearing on sub-pages

I’m a pretty inexperienced programmer but I recently made my first github pages. In order to file my posts I set up multiple pages by creating new markdown files such as project1.md with yaml frontmatter(with the triple dashes ofc):

layout: page
title: “project1”
permalink: /project1/

This worked for creating additional pages that I could link to and reach from my main page but the theme defined in the auto-generated _config.yml file wouldn’t appear for those pages.
I tried alternate configurations of the frontmatter like

layout: page
title: “project1”
permalink: /project1/
theme: jekyll-theme-minimal

or the same as above but swapping page for default, to no avail.
What am I missing? How can I get the theme to propagate to sub-pages?

Have you tried adding a 404 page? That one carried the theme for me. Just as a test to see if some weird setting is active.

Has this been resolved? I have the same issue — but the 404 page works fine.