How to fix the error `found no layout file for “HTML” for “page”` in Hugo CMS?

Okay so here is what is likely happening:

You have a theme you added as a git submodule and you recently re-cloned your project. Guess what? Your submodule needs to be re-downloaded as well.

You can do this with:

git submodule init
git submodule update

Then your project will load without errors.