Last addition, just in case anyone needs this and to be completely fair to DO. DigitalOcean got back to me again about this, and they’re now aware of the issue and plan to update the buildpacks. However, they did also provide a way of getting Hugo to work with a Dockerfile.
Create a Dockerfile in the root of the project with the following content:
FROM peaceiris/hugo:v0.113.0-mod
WORKDIR /app
COPY . /app
RUN hugo -d public
You can also use FROM peaceiris/hugo:latest-mod to use the latest version.
Create a new app, edit components, set it to a static site (it’ll default to an app with a monthly cost but the static site will be free), then set the output directory to /app/public.
They say this should work but I haven’t had time to test it. But it’s nice to see that DO are working on it.